The basis of the Christian faith is the belief that a historical person who lived in the first century of the Common Era (CE), Jesus of Nazareth, was and is the "Christ" (from the Greek meaning "the one anointed" (by God)). This means, in Christian belief, that Jesus is both a human person and God incarnate.
The significance of the incarnation is that through his acceptance of human life and death by execution, and especially his resurrection from the dead, Jesus Christ liberates all of creation from the power of evil. Even more, Christians believe that Christ's resurrection allows any individual to become united to God in a way that was not possible before that event.
As God, Christ (Jesus) is understood specifically to be one of three interrelated facets or (somewhat misleadingly) "persons" of the divine. God is thus very frequently referred to as the "Holy Trinity", being the Father, Son (i.e. Christ) and Holy Spirit. The Holy Spirit is understood to be spiritually present in all things and as a result intimately accessible to every person.
Understanding the historical and theological context of the life of Jesus is very important to understanding the Christian faith. In particular, Jesus was a Jew, and framed his teachings in terms that accorded with the cultural environment of first-century Judaism. This is not considered accidental by Christians: rather, they believe that Jesus is the fulfillment of the teachings and prophecies of the Jewish faith: in Jewish terms, he is the Messiah. For Christians, the Jewish scriptures (especially the Psalms and the books of the prophets) give substantial support to this contention.
Much more important to most Christians than the Jewish scriptures (which are collectively referred to by Christians as the "Old Testament") is a shorter collection of works compiled in the decades following Christ's resurrection. This "New Testament" consists mainly of accounts of the life and teachings of Jesus and letters to early Christian communities and individuals. Christians' attitudes toward the New Testament vary greatly, but almost all would agree that it is a principal source for their knowledge of Christ.
Another basic source, at least for those known as Orthodox Christians and Catholic Christians, is the accumulated tradition of the Christian Church. That view of the importance of tradition is closely linked to those Christians' understanding of the Church itself, which differs significantly from the understanding held by most of those known as Protestant Christians. Very briefly, the Catholic and Orthodox ascribe to the Church a more directive and more authoritative function than do Protestants, who instead tend to emphasize the importance of individual decision-making in both doctrinal and institutional matters.
One point on which virtually all Christians agree is that their faith is not, despite the way it is often misrepresented in modern popular culture, simply a set of rules for moral living. The teachings of Jesus have important ethical components, and Christians are expected to live up to high standards of personal and social behavior. But it is the personal transformation of the individual that is the goal; in New Testament terms, the realization that "the Kingdom of Heaven is within you" (alternatively translated "among you").
Similarly, Christianity is often dismissed as being about "pie in the sky when we die" -- that is, a promise that following certain rules in this life will buy an eternal life in heaven after death, and a threat that failing to follow the rules ("sinning") will condemn one to eternal torment in hell. This view of God as an implacable, rule-bound judge is especially common in those cultures where the dominant form of Christianity has been the "Western" (Catholic and/or Protestant) form, but it is not a fair characterization even of those traditions. Rather, Christians of all kinds understand God more as a perfectly loving parent, and sin more as a sort of self-imposed illness. Indeed, one early Christian prayer addresses God as "the physician of our souls and bodies".
The global spread of Christianity is objectively attributable to several factors, not least the success of European cultures in subjugating and displacing many of the world's indigenous cultures. Even before the age of colonialism, however, Christianity experienced a remarkable dispersion. For example, among the earliest Christian communities are those in Ethiopia and Armenia. Early missions also reached China and India in the East, and Ireland in the West. This expansion reflects the importance in the Christian religion of "evangelism", or spreading the faith.