Why is Jesus called "Christ"?

Because "Christ" began as a title, not a surname: it is the Greek form (Christos) of the Hebrew "Messiah," which means "anointed one" — God's anointed king. Jewish hope in Jesus' day was not one thing, but where a deliverer was hoped for, in its most familiar form he was a son of David who would restore Israel. To say "Jesus Christ" is, at root, to say "Jesus the Messiah." The disciples were named after the title: "The disciples were first called Christians at Antioch" (Acts 11:26), and the Roman historian Tacitus, describing Nero's persecution after the fire of AD 64, explains the group's name by its founder, "Christus." How often "Christ" works as a title rather than a name in Paul is debated; even those who judge it largely a proper name there, as Dahl and Hengel do, hold that it presupposes the claim that Jesus is the Messiah.

On its own, "Messiah" did not mean "divine": a first-century Jew could hope for an anointed king while holding the strictest monotheism. The New Testament fills the title fuller, and the church confesses the Messiah as the eternal Son, fully God and fully man. What the title came to mean, beside Jesus' other titles, is taken up in the deep dive; whether Jesus himself claimed it is answered in "Did Jesus Claim to Be the Messiah?"