What is the X in X-mas?
c.1300, cristente, "Christians as a whole; state of being a Christian," from Old French crestienté "Christendom; spiritual authority; baptism" (Modern French chrétienté), from Church Latin christianitatem (nominative christianitas), noun of state from christianus (see Christian). Gradually respelled to conform with Latin. Christendom is the older word for it. Old English also had cristennes.
The religion based on the life and teachings of Jesus Christ. Christians believe that Jesus Christ is the Messiah, sent by God. They believe that Jesus, by dying and rising from the dead, made up for the sin of Adam and thus redeemed the world, allowing all who believe in him to enter heaven. Christians rely on the Bible as the inspired word of God. (See also gospel, Nativity, Resurrection, salvation, and Sermon on the Mount.)