Christianity is a monotheistic religion founded by the followers of Jesus of Nazareth. Jesus, a Jew, was born in about 7 B.C. and assumed his public life, probably after his 30th year, in Galilee. The New Testament Gospels describe Jesus as a teacher and miracle worker. He proclaimed the kingdom of God, a future reality that is at the same time already present. Jesus set the requirements for participation in the kingdom of God as a change of heart and repentance for sins, love of God and neighbor, and concern for justice. Circa A.D. 30 he was executed on a cross in Jerusalem, a brutal form of punishment for those considered a political threat to the Roman Empire.
After his death his followers came to believe in him as the Christ, the Messiah. The Gospels report his resurrection and how the risen Jesus was witnessed by many of his followers. The apostle Paul helped spread the new faith in his missionary travels. Historically, Christianity arose out of Judaism and claims that Jesus fulfilled many of the promises of the Hebrew Scripture (often referred to as the Old Testament).
The new religion spread rapidly throughout the Roman Empire. In its first two centuries, Christianity began to take shape as an organization, developing distinctive doctrine, liturgy, and ministry. By the fourth century the Christian church had taken root in countries stretching from Spain in the West to Persia and India in the East. Christians had been subject to persecution by the Roman state, but gained tolerance under Constantine the Great (A.D. 313). The church became favored under his successors, and in 380 the emperor Theodosius proclaimed Christianity the state religion. Other religions were suppressed.
Because differences in doctrine threatened to divide the church, a standard Christian creed was formulated by bishops at successive ecumenical councils, the first of which was held in A.D. 325 (Nicaea). Important doctrines were defined concerning the Trinity—in other words, that there is one God in three persons: Father, Son, and Holy Spirit (Constantinople, A.D. 381), and the nature of Christ as both divine and human (Chalcedon, A.D. 541). Christians came to accept both Hebrew Scripture and the New Testament as authoritative. The New Testament comprises four Gospels (narratives of Jesus' life), 21 Epistles, The Acts of the Apostles, and Revelation.
Because of differences between Christians of the East and West, the unity of the church was broken in 1054. The religious center for the Eastern Orthodox Church was Constantinople, and the Roman Catholic Church defined doctrine and practice for Christians in the West. In 1517 the Reformation began, which ultimately caused a schism in the Western church. Reformers wished to correct certain practices within the Roman church, but they also came to view the Christian faith in a distinctly new way. The major Protestant denominations (Lutheran, Presbyterian, Reformed, and Anglican [Episcopalian]) thus came into being. Over the centuries, numerous denominations have broken with these major traditions, resulting in a spectrum of Christian expression.
In the 21st century, many Christians hope to regain a sense of unity through dialogue and cooperation among different traditions. The ecumenical movement led to the formation of the World Council of Churches in 1948 (Amsterdam), which has since been joined by many denominations.
Through its missionary activity Christianity has spread to most parts of the globe.