St. Luke was not a Jew. He is separated by St. Paul from those of the circumcision (Col.4:14), and his style proves that he was a Greek. Hence he cannot be identified with Lucius the prophet of Acts 3:1, nor with Lucius of Rom 16:21, who was a relative of St. Paul. He was not one of the Seventy Disciples; nor was he the companion of Cleophas in the journey to Emmaus after the Resurrection (as some scholars believe). St. Luke had a great knowledge of the Septuagint (the Greek Old Testament) and of things Jewish, which he acquired either as a Jewish proselyte (according to St. Jerome) or after he became a Christian, through his close intercourse with the Apostles and disciples. Besides Greek, he had many opportunities of acquiring Aramaic in his native Antioch, the capital of Syria. He was a physician by profession, and St. Paul calls him “the most dear physician” (Colossians 4:14). This avocation implied a liberal education, and his medical training is evidenced by his choice of medical language. He may have studied medicine at the famous school of Tarsus, the rival of Alexandria and Athens, and possibly met St. Paul there. From his intimate knowledge of the eastern Mediterranean, it has been conjectured that he had lengthened experience as a doctor on board ship. He traveled a good deal, and sends greetings to the Colossians, which seems to indicate that he had visited them.
St. Luke first appears in the Acts at Troas (16:8), where he meets St. Paul, and, then crosses over with him to Europe as an Evangelist, landing at Neapolis and going on to Philippi, “being assured that God had called us to preach the Gospel to them” (note especially the transition into first person plural at verse 10). He was, therefore, already an Evangelist.
He was present at the conversion of Lydia and her companions, and lodged in her house. He, together with St. Paul and his companions, was recognized by the evil spirit: “This same following Paul and us, cried out, saying: These men are the servants of the most high God, who preach unto you the way of salvation” (verse 17). He was present when Paul and Silas were arrested, dragged before the Roman magistrates, charged with disturbing the city, “being Jews”, beaten with rods and thrown into prison.
Luke and Timothy escaped, probably because they did not look like Jews (Timothy’s father was a gentile). When Paul departed from Philippi, Luke was left behind, in all probability to carry on the work of Evangelist. At Thessalonica St. Paul received highly appreciated monetary aid from Philippi (Phil. 4:15, 16), doubtless through the good offices of St. Luke. It is not unlikely that the latter remained at Philippi all the time that St. Paul was preaching at Athens and Corinth, and while he was traveling to Jerusalem and back to Ephesus, and during the three years that St. Paul was at Ephesus.
When St. Paul revisited Macedonia, he again met St. Luke at Philippi, and there wrote his Second Epistle to the Corinthians St. Luke is always represented by the calf or ox, the sacrificial animal, because his Gospel begins with the account of Zachary the priest, the father of John the Baptist. St. Luke is one of the most extensive writers of the New Testament. His Gospel is considerably longer than St. Matthew’s, his two books are about as long as St. Paul’s fourteen Epistles; and Acts exceeds in length the Seven Catholic Epistles and the Book of Revelation. It is clear from his Gospel that he was well acquainted with the Gospel according to St. Mark; and in the Acts he knows all the details of St. Peter’s delivery–what happened at the house of St. Mark’s mother, and the name of the girl who ran to the outer door when St. Peter knocked. He must have frequently met St. Peter, and may have assisted him in writing his First Epistle in Greek, which affords many reminiscences of Luke’s style. St. Luke is a painter in words. The style of his Gospel is superior to any N.T. writing except Hebrews. Some scholars say that it is the most literary of the Gospels. It is known that he remained a bachelor all of his life, devoting himself to the utmost degree to the cause of Christ. He died in Thebes at the age of seventy-four. (Paraphrased from Internet sources, esp. the Catholic Encyclopedia).