What is Christianity? Beliefs, Bible and branches, explained

Christianity is the religion based on the life and teaching of Jesus of Nazareth, whom Christians believe to be the Son of God, who died on a cross and rose from the dead to reconcile people with God. It began as a movement within Judaism in the 1st century CE and is today the world's largest religion, with about 2.3 billion followers in 2020, in three main branches: Catholic, Orthodox and Protestant.

In short

• Christians hold that one God exists as three persons, Father, Son and Holy Spirit, and that Jesus is God become human.
• At the center of the faith is Jesus's death and resurrection, which Christians believe offers salvation, forgiveness and eternal life.
• The Bible joins the Hebrew scriptures, as the Old Testament, to 27 books about Jesus and the first churches, the New Testament.

What do Christians believe?

Christians hold a shared core, summed up in the creeds that most churches recite. The best known, the Nicene Creed, was first drafted at a council of bishops at Nicaea in 325 CE and expanded in 381.

• One God in three persons. Christians believe in one God who is Father, Son and Holy Spirit, the Trinity. They do not count three gods; they hold that the one God exists eternally in three persons (BBC Religions).
• Jesus as God made flesh. The Son became human as Jesus, fully God and fully human, a doctrine called the incarnation. Christians call him the Christ, from the Greek for the Hebrew "messiah", the anointed one.
• The cross and the resurrection. Christians believe Jesus's death on a Roman cross dealt with human sin, and that he rose from the dead on the third day. For Christians, the resurrection is not a side detail but the claim the whole faith rests on.
• Salvation. People are restored to God through faith in Christ, by God's grace. Churches differ on how faith, good works and the sacraments relate.
• The end. Christians expect Christ to return, the dead to be raised and the world to be judged and renewed.

What can be said of Jesus as a figure of history, and how that differs from what Christians believe, is the subject of who Jesus was.

How was the Bible put together?

The Bible was assembled over centuries, not written as one book. Its first part, the Old Testament, is the scripture of Judaism, the Hebrew Bible, which the first Christians, Jews themselves, read as pointing to Jesus. The second part, the New Testament, holds 27 books written in Greek between about 50 and 120 CE: four Gospels about Jesus's life, the Acts of the Apostles, letters, many by Paul, the earliest Christian writings, and the book of Revelation.

The list of books, the canon, settled gradually. Churches read many writings in the 2nd and 3rd centuries and argued over some, such as Revelation and Hebrews. In 367 CE, Athanasius, bishop of Alexandria, sent a letter listing exactly today's 27 New Testament books, and councils in North Africa at Hippo in 393 and Carthage in 397 confirmed a similar list. The Old Testament still differs between churches: Catholic and Orthodox Bibles include books, such as Tobit and the Maccabees, that most Protestant Bibles leave out or print separately as the Apocrypha.

How did Christianity divide?

Christianity spread through the Roman Empire, at first as a sometimes persecuted minority, until the emperor Constantine favored it from 312 and it became the empire's official religion in 380. The great divisions came later.

Year	What happened
c. 30–33 CE	Jesus is crucified in Jerusalem; his followers proclaim his resurrection
c. 50–60	Paul writes letters to new churches around the Mediterranean, many of them non-Jewish
325	The Council of Nicaea; its creed defines the Son as one in being with the Father
451	The Council of Chalcedon; churches that reject its definition of Christ's two natures form the Oriental Orthodox churches, such as the Coptic and Armenian
1054	The East–West Schism: the churches of Rome and Constantinople excommunicate each other's leaders, over the pope's authority and a phrase added to the creed in the West
1517	Martin Luther publishes his Ninety-five Theses, beginning the Protestant Reformation
1534	The Church of England breaks with Rome under Henry VIII
1906	The Azusa Street revival in Los Angeles helps launch Pentecostalism
1965	The pope and the patriarch of Constantinople lift the 1054 excommunications

The 1054 schism hardened over the following centuries, sealed in many minds when crusaders sacked Constantinople in 1204. The Reformation began as a protest about selling indulgences, release from punishment for sin, and became a dispute about authority: whether scripture alone governs the church, and whether people are saved by faith alone.

How do Catholics, Orthodox and Protestants differ?

The three branches share the creeds and the Trinity. They differ most over authority, sacraments and how salvation is received.

	Catholic	Orthodox	Protestant
Followers, 2010	About 1.1 billion, 50% of Christians	About 260 million, 12%	About 801 million, 37%, including Anglicans and independent churches
Authority	Scripture and tradition, taught by bishops under the pope	Scripture and tradition, held by bishops in council; the patriarch of Constantinople is first among equals	Scripture alone; no central authority
Sacraments	Seven, with the Mass at the center	Seven, called mysteries, with the Divine Liturgy at the center	Usually two, baptism and the Lord's Supper
Clergy	Priests, usually unmarried in the Latin church	Priests may marry before ordination; bishops are monks	Ministers or pastors, who may marry; many churches ordain women
Salvation	By grace, received through faith, sacraments and works of love	Theosis: becoming united with God by grace	By grace through faith alone
Mary and the saints	Prayers to saints; doctrines of Mary's immaculate conception and assumption	Icons and saints are honored; Mary, the Theotokos, is venerated	Saints honored as examples, generally not prayed to

The figures are Pew Research Center's estimates for 2010, from its last detailed count by branch (Pew Research Center, 2011). About 1% of Christians belong to groups outside the three, such as Latter-day Saints and Jehovah's Witnesses. Protestantism itself holds thousands of denominations, from Lutherans, Anglicans and Baptists to Methodists and Pentecostals, which differ on baptism, church government and worship.

How do Christians practice their faith?

Christian practice centers on Sunday worship, chosen as the day of the resurrection. In most churches it includes readings from the Bible, prayer, singing, a sermon and, often, communion, the sharing of bread and wine that Jesus asked his followers to repeat at his last meal. Baptism, with water, marks entry into the church, whether as an infant or, in Baptist and many other churches, as a believer. The Lord's Prayer, which the Gospels say Jesus taught, is shared by nearly all.

The year turns on two feasts. Christmas marks Jesus's birth, after four weeks of Advent. Easter, the most important, marks the resurrection, after the 40 days of Lent and the Holy Week that recalls his last supper and crucifixion. Orthodox churches usually celebrate Easter on a different date because they calculate it by the older Julian calendar. Christian moral teaching grows from Jesus's two great commandments, to love God and one's neighbor, and has generated traditions of its own, such as the medieval list of seven deadly sins.

Where do Christians live today?

Christianity remains the largest religion, but its center of gravity has moved south. Pew Research Center found that in 2020, 30.7% of the world's Christians lived in sub-Saharan Africa, compared with 22.3% in Europe, and that the Christian share of the world's population fell between 2010 and 2020 to 28.8%, mainly because of disaffiliation, people raised Christian who now identify with no religion (Pew Research Center, 2025). How Christianity compares with other faiths, and what scholars mean by religion at all, are questions of their own.

Check yourself

• What do Christians mean by the Trinity, and why do they say it is not three gods?
• Why did the churches of Rome and Constantinople split in 1054, and what did Luther challenge in 1517?
• Name one difference in authority and one in sacraments between Catholics, Orthodox and Protestants.

Sources

• How the Global Religious Landscape Changed From 2010 to 2020 — Pew Research Center, 2025
• Global Christianity: Christian traditions — Pew Research Center, 2011
• The Trinity — BBC Religions, 2011
• Christianity — World History Encyclopedia, Rebecca Denova
• East–West Schism — Wikipedia
• Biblical canon — Wikipedia