The word Jesus is the Latin form of the Greek Iesous, which in turn is the transliteration of the Hebrew Jeshua, or Joshua, or again Jehoshua, meaning "Jehovah is salvation." Though the name in one form or another occurs frequently in the Old Testament, it was not borne by a person of prominence between the time of Josue, the son of Nun and Josue, the high priest in the days of Zorobabel. It was also the name of the author of Ecclesiaticus, of one of Christ's ancestors mentioned in the genealogy, found in the Third Gospel (Luke 3:29), and one of the St. Paul's companions (Colossians 4:11). During the Hellenizing period, Jason, a purely Greek analogon of Jesus, appears to have been adopted by many (1 Maccabees 8:17; 12:16; 14:22; 2 Maccabees 1:7; 2:24; 4:7-26; 5:5-10; Acts 17:5-9; Romans 16:21). The Greek name is connected with verb iasthai, to heal; it is therefore, not surprising that some of the Greek Fathers allied the word Jesus with same root (Eusebius, "Dem. Ev.", IV; cf. Acts 9:34; 10:38). Though about the time of Christ the name Jesus appears to have been fairly common (Josephus, "Ant.", XV, ix, 2; XVII, xiii, 1; XX, ix, 1; "Bel. Jud.", III, ix, 7; IV, iii, 9; VI, v, 5; "Vit.", 22) it was imposed on our Lord by God's express order (Luke 1:31; Matthew 1:21), to foreshow that the Child was destined to "save his people from their sins." Philo ("De Mutt. Nom.", 21) is therefore, right when he explains Iesous as meaning soteria kyrion; Eusebius (Dem., Ev., IV, ad fin.; P.G., XXII, 333) gives the meaning Theou soterion; while St. Cyril of Jerusalem interprets the word as equivalent to soter (Catechetical Lectures X.13). This last writer, however, appears to agree with Clement of Alexandria in considering the word Iesous as of Greek origin (The Pedagogue III.12); St. Chrysostom emphasizes again the Hebrew derivation of the word and its meaning soter (Homily 2 on Matthew, No. 2), thus agreeing with the exegesis of the angel speaking to St. Joseph (Matthew 1:21).
The word Christ, Christos, the Greek equivalent of the Hebrew Messias, means "anointed." According to the Old Law, priests (Exodus 29:29; Leviticus 4:3), kings (1 Samuel 10:1; 24:7), and prophets (Isaiah 61:1) were supposed to be anointed for their respective offices; now, the Christ, or the Messias, combined this threefold dignity in His Person. It is not surprising, therefore, that for centuries the Jews had referred to their expected Deliverer as "the Anointed"; perhaps this designation alludes to Isaias 61:1, and Daniel 9:24-26, or even to Psalms 2:2; 19:7; 44:8. Thus the term Christ or Messias was a title rather than a proper name: "Non proprium nomen est, sed nuncupatio potestatis et regni", says Lactantius (Divine Institutes IV.7). The Evangelists recognize the same truth; excepting Matthew 1:1, 1:18; Mark 1:1; John 1:17; 17:3; 9:22; Mark 9:40; Luke 2:11; 22:2, the word Christ is always preceded by the article.
Only after the Resurrection did the title gradually pass into a proper name, and the expression Jesus Christ or Christ Jesus became only one designation. But at this stage the Greeks and Romans understood little or nothing about the import of the word anointed; to them it did not convey any sacred conception. Hence they substituted Chrestus, or "excellent", for Christus or "anointed", and Chrestians instead of "Christians." There may be an allusion to this practice in 1 Peter 2:3; hoti chrestos ho kyrios, which is rendered "that the Lord is sweet." Justin Martyr (First Apology 4), Clement of Alexandria (Stromata II.4.18), Tertullian (To the Nations II), and Lactantius (Divine Institutes IV.7), as well as St. Jerome (In Gal., V, 22), are acquainted with the pagan substitution of Chrestes for Christus, and are careful to explain the new term in a favourable sense. The pagans made little or no effort to learn anything accurate about Christ and the Christians; Suetonius, for instance, ascribes the expulsion of the Jews from Rome under Claudius to the constant instigation of sedition by Chrestus, whom he conceives as acting in Rome the part of a leader of insurgents.
The use of the definite article before the word Christ and its gradual development into a proper name show the Christians identified the bearer with the promised Messias of the Jews. He combined in His person the offices of prophet (John 6:14; Matthew 13:57; Luke 13:33; 24:19) of king (Luke 23:2; Acts 17:7; 1 Corinthians 15:24; Apocalypse 15:3), and of priest (Hebrews 2:17; etc.); he fulfilled all the Messianic predictions in a fuller and a higher sense than had been given them by the teachers of the Synagogue.
(Taken from the Catholic Encyclopedia)