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What Is Christianity?

Christianity is a monotheistic religion based on the life, teachings, death, and resurrection of Jesus of Nazareth, whom followers believe to be the Son of God and the Messiah (Christ) prophesied in the Hebrew scriptures. With approximately 2.4 billion adherents worldwide as of 2024, it is the largest religion on Earth, shaping laws, cultures, art, philosophy, and politics across every continent for nearly two thousand years.

The Core Story: Jesus of Nazareth

You can’t understand Christianity without understanding Jesus. Born around 4 BCE in Roman-occupied Judea (the dating is slightly off because the monk who calculated the calendar made a math error—yes, really), Jesus grew up in Nazareth, a small town in Galilee. He was Jewish, raised in Jewish tradition, and began his public ministry around age 30.

For roughly three years, Jesus traveled through the region teaching, performing what followers describe as miracles (healing the sick, feeding crowds, raising the dead), and gathering disciples. His teachings were often delivered in parables—short stories with spiritual or moral lessons. The Good Samaritan, the Prodigal Son, the Sower and the Seed—these stories have become so embedded in Western culture that people reference them without knowing their origin.

What made Jesus controversial wasn’t just his teachings—it was his claims. He claimed a unique relationship with God, forgave sins (something only God could do in Jewish theology), and challenged religious authorities. The established religious leaders saw him as a threat. The Roman authorities saw a potential revolutionary.

Around 30-33 CE, Jesus was arrested, tried, and executed by crucifixion under the Roman governor Pontius Pilate. And that would have been the end of the story—another failed messianic claimant in a region full of them—except for what his followers claimed happened next.

The Resurrection: Christianity’s Central Claim

The resurrection of Jesus is the foundational claim of Christianity. His followers reported that three days after his execution, his tomb was empty and he appeared to them alive over a period of 40 days before ascending to heaven. The apostle Paul, writing around 55 CE (roughly 20 years after the events), stated that Jesus appeared to more than 500 people at once.

This is the claim that either makes or breaks Christianity. As Paul himself wrote: “If Christ has not been raised, our preaching is useless and so is your faith.” Christians don’t present the resurrection as a metaphor or a spiritual truth—mainstream Christian theology insists it was a physical, historical event.

Whether you accept this claim is, of course, a matter of faith. But understanding that Christianity stands or falls on this specific historical assertion helps explain why it’s so central to Christian identity.

What Christians Actually Believe

Christian theology is vast—two thousand years of thinkers will produce a lot of ideas. But certain core beliefs are shared across most Christian traditions.

God as Trinity

Most Christians believe in the Trinity: one God existing as three distinct persons—Father, Son (Jesus), and Holy Spirit. This isn’t three gods (that would be polytheism) or one God wearing three masks (that’s the heresy called modalism). It’s something more subtle and, frankly, hard to fully grasp—three distinct persons sharing one divine essence.

The Trinity wasn’t spelled out neatly in the Bible. It was developed over centuries of theological debate, formally defined at the Council of Nicaea in 325 CE and further clarified at the Council of Constantinople in 381 CE. The Nicene Creed, still recited in many churches today, codifies these beliefs.

Sin and Salvation

Christianity teaches that humanity is separated from God by sin—not just individual bad actions, but a fundamental brokenness inherited from the earliest humans (the doctrine of original sin, particularly emphasized in Western Christianity). Humans can’t fix this separation through their own efforts.

The Christian answer to this problem is grace—God’s unmerited favor, extended through Jesus’s death and resurrection. By dying on the cross, Jesus took the penalty for human sin upon himself, making reconciliation with God possible. This is called atonement, and Christians have debated its precise mechanics for centuries. Did Jesus pay a ransom? Satisfy divine justice? Defeat the powers of evil? Different theories emphasize different aspects.

How individuals receive this salvation varies by tradition. Some emphasize faith alone (sola fide)—believing and trusting in Jesus is sufficient. Others add works—faith must produce action to be genuine. Still others emphasize sacraments—baptism and communion as channels of grace. These differences drive many of the divisions between denominations.

The Afterlife

Most Christians believe in an afterlife involving heaven (eternal communion with God) and hell (eternal separation from God). The specifics vary enormously. Some traditions describe literal, physical places. Others understand them more metaphorically. Some believe in purgatory—a state of purification before heaven (primarily a Catholic doctrine). A minority hold to annihilationism—that the unsaved simply cease to exist rather than suffering eternally.

The Second Coming—Jesus’s prophesied return to Earth—is another widely held belief. Most Christians expect Jesus to return, judge the living and dead, and establish God’s kingdom fully. When and how this happens is the subject of intense debate and an entire subfield of theology called eschatology.

The Bible: Christianity’s Sacred Text

The Bible is Christianity’s scripture, but calling it “a book” is misleading. It’s a library—66 books (73 in Catholic Bibles, which include the deuterocanonical texts) written by dozens of authors over roughly 1,500 years in three languages (Hebrew, Aramaic, and Greek).

The Old Proof

The Old Proof (or Hebrew Bible) contains the sacred scriptures Christianity inherited from Judaism. It includes creation narratives, historical accounts, legal codes, poetry (Psalms, Song of Solomon), wisdom literature (Proverbs, Ecclesiastes), and prophetic writings. Christians read these texts through a christological lens—seeing prophecies and foreshadowing of Jesus throughout.

The New Proof

The New Proof is specifically Christian scripture, written in the decades following Jesus’s life. It contains:

• The Gospels (Matthew, Mark, Luke, John): Four accounts of Jesus’s life, teachings, death, and resurrection. They’re not identical—each author had a different audience, emphasis, and theological perspective. Mark is the shortest and probably earliest. John is the most theological and differs significantly from the other three (called the “Synoptic” Gospels because they share so much material).

• Acts of the Apostles: The history of the early church after Jesus’s ascension, focusing on the ministries of Peter and Paul.

• The Epistles: Letters written by Paul and other early leaders to churches and individuals. Romans, Corinthians, Galatians—these letters address specific theological questions and practical problems. Much of Christian theology comes from Paul’s letters rather than directly from Jesus’s recorded words.

• Revelation: An apocalyptic text describing visions of the end times. It’s the most debated book in the Bible, with interpretations ranging from literal prophecy to symbolic commentary on the Roman Empire.

How Christians Read the Bible

This is where things get complicated. Christians don’t agree on how to interpret their own scripture. Some hold to biblical literalism—every word is historically and scientifically accurate. Others practice historical-critical interpretation—analyzing texts in their original cultural and literary context. Still others read allegorically or typologically, finding spiritual meanings beyond the surface text.

These different approaches produce radically different conclusions on everything from the age of the Earth to the role of women in church leadership. The same text, read by different Christians with different interpretive frameworks, yields genuinely different theologies.

The Major Branches: A Family Tree

Christianity’s 2.4 billion adherents are distributed across thousands of denominations, but three major branches contain the vast majority.

Roman Catholicism (~1.3 billion)

The Catholic Church is the largest single Christian denomination, led by the Pope in Rome, who Catholics believe holds authority passed down from the apostle Peter. Catholicism emphasizes tradition alongside Scripture, seven sacraments (baptism, confirmation, Eucharist, penance, anointing of the sick, holy orders, and matrimony), and the authority of the Church’s teaching office (Magisterium).

Catholic worship centers on the Mass—a liturgical service culminating in the Eucharist, which Catholics believe becomes the actual body and blood of Christ (transubstantiation). The veneration of saints, devotion to Mary (the mother of Jesus), and a structured hierarchy of deacons, priests, bishops, and cardinals distinguish Catholicism from most Protestant traditions.

Eastern Orthodoxy (~220 million)

The Orthodox Church split from Roman Catholicism in the Great Schism of 1054 CE, primarily over papal authority and a theological clause in the Nicene Creed (the filioque controversy—whether the Holy Spirit proceeds from the Father alone or from both Father and Son). Orthodox Christianity is organized into autocephalous (self-governing) churches—Greek Orthodox, Russian Orthodox, Serbian Orthodox, and others.

Orthodox worship is intensely liturgical, rich with icons (sacred images used in prayer and contemplation—not worshipped, but venerated), incense, and chanting. The aesthetics of Orthodox worship are deliberately designed to create a sense of heaven on earth. Orthodox theology emphasizes theosis—the process of becoming more like God through prayer, sacraments, and spiritual practice.

Protestantism (~900 million)

Protestantism began in 1517 when Martin Luther nailed his 95 Theses to a church door in Wittenberg, Germany (or possibly just mailed them to his bishop—the dramatic door-nailing might be legend). Luther objected to the sale of indulgences and other Catholic practices he considered unbiblical.

The Protestant Reformation produced several core principles: sola scriptura (Scripture alone as the ultimate authority), sola fide (faith alone for salvation), sola gratia (grace alone), and the priesthood of all believers (no special priestly class needed to access God).

But Protestantism immediately fragmented. Luther’s followers became Lutherans. John Calvin’s teachings produced Reformed/Presbyterian traditions. The Anabaptists rejected infant baptism. The Church of England split from Rome for partly political reasons. Over centuries, these branches continued dividing—Baptists, Methodists, Pentecostals, Adventists, and thousands more.

Today, the fastest-growing Christian movements are Pentecostal and Charismatic—emphasizing direct experience of the Holy Spirit, speaking in tongues, faith healing, and energetic worship. These movements are particularly strong in Africa, Asia, and Latin America.

Christianity’s Historical Impact

Christianity’s influence on world history is almost impossible to overstate. For better and worse, it shaped civilization.

Positive Contributions

Christian institutions founded many of the world’s oldest universities—Oxford, Cambridge, Paris, Bologna. Monasteries preserved classical learning through the medieval period. Christian ethics influenced the development of human rights concepts, the abolition of slavery (many abolitionists were motivated by Christian conviction), and the establishment of hospitals and charitable organizations.

The artistic legacy is staggering. Christian patronage produced Michelangelo’s Sistine Chapel ceiling, Bach’s Mass in B Minor, Dante’s Divine Comedy, Gothic cathedrals, Orthodox iconography, and centuries of Western art and music. The study of aesthetics in Western philosophy is inseparable from Christian artistic tradition.

Painful History

Honesty requires acknowledging Christianity’s darker chapters. The Crusades (1096-1291) launched military campaigns that killed thousands. The Inquisitions persecuted alleged heretics, Jews, and others. European colonialism often justified itself through Christian missionary ideology, destroying indigenous cultures and enabling exploitation. Denominational conflicts—Catholic vs. Protestant, Orthodox vs. Catholic—produced wars, persecution, and lasting social divisions.

The relationship between Christianity and science has been complicated. The Galileo affair (the Church’s condemnation of heliocentrism) is the most famous example, though the historical reality is more nuanced than the popular narrative suggests. Many pioneering scientists—Copernicus, Mendel, Lemaitre—were themselves clergy.

Christianity and Philosophy

Christian theology and Western philosophy have been in conversation for two millennia. Early Church Fathers like Augustine of Hippo (354-430 CE) synthesized Christian theology with Neoplatonic philosophy. Thomas Aquinas (1225-1274) integrated Aristotelian philosophy with Christian doctrine, producing Scholasticism—the dominant intellectual framework of medieval Europe.

The stoicism of Roman philosophy influenced early Christian ethics, particularly in its emphasis on virtue, self-discipline, and acceptance of suffering. Paul’s letters show familiarity with Stoic concepts, and many early converts came from philosophical backgrounds.

The Enlightenment challenged Christianity’s intellectual dominance, but Christian philosophy didn’t disappear—it adapted. Kierkegaard developed Christian existentialism. C.S. Lewis wrote popular apologetics. Liberation theology in Latin America connected Christian faith to social justice. Today, philosophy of religion remains an active academic field, with Christian philosophers contributing to debates about consciousness, ethics, and the existence of God.

Christianity in the Modern World

Contemporary Christianity is shifting geographically and culturally. In 1900, roughly 80% of Christians lived in Europe and North America. By 2025, that figure has dropped below 40%. The global center of Christianity has moved south and east—Africa, Asia, and Latin America now contain the majority of the world’s Christians.

This shift brings different emphases. African and Asian Christianity tends to be more supernaturalist, more community-oriented, and more conservative on social issues than the increasingly secular Christianity of Western Europe. Pentecostalism, with its emphasis on direct spiritual experience, resonates particularly strongly in cultures with existing spiritual traditions.

In the West, Christianity faces declining membership in many denominations—a phenomenon sociologists call secularization. Church attendance in Western Europe has dropped dramatically since the mid-20th century. The United States, historically an outlier for its high religiosity, has seen a significant rise in “nones”—people claiming no religious affiliation—particularly among younger generations.

Yet Christianity isn’t simply declining. It’s changing shape. Megachurches draw thousands of weekly attendees. Online worship expanded dramatically during the COVID-19 pandemic. Social media creates new forms of religious community. House churches in countries where Christianity faces persecution demonstrate remarkable resilience and growth.

Christian Ethics and Social Teaching

Christianity has produced rich traditions of ethical thinking. The Sermon on the Mount (Matthew 5-7)—with its teachings on turning the other cheek, loving enemies, and caring for the poor—provides an ethical framework that even non-Christians often admire.

Catholic Social Teaching, developed through papal encyclicals since 1891, addresses economic justice, workers’ rights, environmental stewardship, and human dignity. Protestant social ethics range from the Social Gospel movement (emphasizing collective social reform) to evangelical emphasis on personal morality and individual transformation.

Christian perspectives on contemporary issues—abortion, LGBTQ+ rights, capital punishment, immigration, war, economic inequality—vary enormously across denominations. There is no single “Christian position” on most modern ethical debates, despite claims from various sides to speak for Christianity as a whole.

The relationship between Christianity and anthropology is important here—how Christians understand human nature shapes their entire ethical framework. If humans are fundamentally fallen, ethics emphasizes redemption and moral boundaries. If humans are fundamentally good but damaged, ethics emphasizes healing and liberation.

Worship and Practice

How Christians worship varies as much as what they believe.

Liturgical traditions (Catholic, Orthodox, Anglican, Lutheran) follow structured worship services with set prayers, readings, and rituals. The church calendar marks seasons—Arrival, Christmas, Lent, Easter, Pentecost—each with specific themes and practices. Sacraments—particularly baptism and communion (the Eucharist/Lord’s Supper)—are central.

Evangelical and free-church traditions tend toward less formal worship. Contemporary music, extended preaching, spontaneous prayer, and personal testimonies characterize many evangelical services. The emphasis falls on personal relationship with God, Bible study, and evangelism (sharing the faith with others).

Contemplative traditions emphasize silence, meditation, and mystical experience. Christian monasticism—dating back to the 3rd century desert fathers and mothers—continues in Benedictine, Cistercian, and other monastic orders. Practices like lectio divina (meditative Scripture reading), centering prayer, and the Jesus Prayer provide alternatives to more verbal worship forms.

Prayer is universal across traditions. Christians pray alone and together—thanking God, asking for help, confessing failings, interceding for others. The Lord’s Prayer (the “Our Father”), taught by Jesus himself according to the Gospels, is the most widely shared prayer in Christianity.

Christianity and Other Religions

Christianity’s relationship with other religions is complex. As a missionary religion, Christianity has historically sought converts worldwide—sometimes through genuine persuasion, sometimes through force and coercion.

Judaism is Christianity’s parent religion. Jesus was Jewish, the apostles were Jewish, and the Old Proof is Jewish scripture. Yet Christianity and Judaism diverged sharply over the question of Jesus’s identity. Anti-Judaism (and later anti-Semitism) in Christian history is a painful reality that modern Christian leaders have increasingly acknowledged and repented of.

Islam recognizes Jesus as a prophet but denies his divinity and crucifixion. Christians and Muslims have had periods of both cooperation and violent conflict throughout history. The Crusades remain a defining memory in Christian-Muslim relations.

Inter-religious dialogue has grown significantly since the mid-20th century. The Catholic Church’s Vatican II council (1962-1965) fundamentally shifted Catholic attitudes toward other religions. The World Council of Churches promotes ecumenical cooperation among Protestant and Orthodox traditions. Yet tensions persist, and some Christians reject dialogue in favor of exclusive truth claims.

Making Sense of Christianity Today

Whether you’re a believer, a skeptic, or simply curious, understanding Christianity matters because its influence is everywhere. Western legal systems, concepts of human rights, educational institutions, artistic traditions, and even the calendar you use all bear Christian fingerprints.

Christianity is neither monolithic nor simple. It contains contemplatives and activists, fundamentalists and progressives, ascetics and prosperity preachers. It has inspired extraordinary acts of compassion and terrible acts of violence. It has produced brilliant philosophy and anti-intellectual obscurantism.

What holds it together—across cultures, centuries, and denominations—is a remarkably specific claim: that a Jewish carpenter from a backwater Roman province was God incarnate, that he died and came back to life, and that this event changed everything. Whether that claim is true is the most consequential question in Christian theology. But even if you conclude it isn’t, the fact that 2.4 billion people believe it—and that this belief has shaped civilization for two millennia—makes Christianity worth understanding on its own terms.

That’s what Christianity is. Not just a set of beliefs or a moral code, but a living tradition—messy, contradictory, sometimes beautiful, sometimes terrible—that continues to shape the world in ways both visible and hidden.

Frequently Asked Questions

How many Christians are there in the world?

As of 2024, there are approximately 2.4 billion Christians worldwide, making Christianity the largest religion by number of adherents. Christians make up roughly 31% of the global population, with significant populations on every inhabited continent.

What is the difference between Catholic and Protestant?

Catholics recognize the Pope as the head of the Church and emphasize tradition alongside Scripture. Protestants, emerging from the 16th-century Reformation, generally reject papal authority and emphasize Scripture alone (sola scriptura) as the basis for faith. There are also significant differences in views on sacraments, saints, and salvation.

Do all Christians believe the same things?

No. While most Christians share core beliefs—the divinity of Jesus, the Trinity, the resurrection—there are thousands of denominations with different views on theology, worship practices, church governance, social issues, and biblical interpretation. The spectrum ranges from highly liturgical traditions to informal charismatic worship.

What is the Holy Trinity?

The Trinity is the Christian doctrine that God exists as three persons—Father, Son (Jesus Christ), and Holy Spirit—who are distinct yet constitute one God. This concept, formally defined in the 4th century, is central to most Christian theology but is not explicitly stated in the Bible, which has made it a subject of ongoing theological discussion.

Is Christianity the oldest religion?

No. Christianity is approximately 2,000 years old, originating in the 1st century CE. Hinduism, Judaism, Zoroastrianism, and several other religions predate it by centuries or millennia. Christianity grew out of Judaism and shares many of its scriptures (the Hebrew Bible/Old Testament).

Further Reading

• Pew Research Center - Global Christianity
• Encyclopedia Britannica - Christianity
• Yale Divinity School Resources
• BBC Religions - Christianity
• Stanford Encyclopedia of Philosophy - Philosophy of Religion