All that we know of Cornelius is contained in the Book of Acts (chapters 10 and 11). A centurion was a Roman army officer, theoretically in charge of a hundred men. Several centurions are mentioned in the New Testament (M 8:5 = L 7:2; M 27:54 = L 23:47; a 10:1; 22:25; 23:17,23; 22:23; 27:1), and they are consistently portrayed favorably.
Cornelius is called a God-fearer--that is to say, he was a monotheist, a Gentile who worshipped the One God. The Jews traditionally recognized that such Gentiles had a place in the Family of God, and they are mentioned along with the priests (House of Aaron), the Levites (House of Levi), and the Jews or Israelites (House of Israel) in Ps 115:9-13, Ps 118:2-4, and Ps 135:19-20. In New Testament times, an estimated ten per cent of the population of the Roman Empire consisted of God-fearers, Gentiles who recognized that the pagan belief in many gods and goddesses, who according to the myths about them were given to adultery, treachery, intrigue, and the like, was not a religion for a thoughtful and moral worshipper, and who had accordingly embraced an ethical monotheism--belief in One God, who had created the world, and who was the upholder of the Moral Law. Although only a few of them took the step of formal conversion to Judaism, undergoing circumcision and accepting the obligations of keeping the food laws and ritual laws of Moses and his rabbinical interpreters, most of them attended synagogue services regularly.
Cornelius, then, was a Roman centurion, and a God-fearing man. One day, as he was praying, an angel appeared to him and told him to send a messenger to Joppa and ask Peter to come and preach to him. Peter, meanwhile, was given a vision that disposed him to go with the messenger. When Peter had preached to Cornelius and his family and friends, the Holy Spirit fell on them, as on the first Christians at Pentecost (A 2), and they began to speak in other tongues. Thus, there was ample evidence to convince Jewish Christians who hesitated to believe that it was the will of God that Gentiles should be brought into the Church.
Cornelius was the first Gentile converted to Christianity, along with his household, and Luke, recording this event, clearly regards it as an event of the utmost importance in the history of the early Church, the beginning of the Church's decision to admit Gentiles to full and equal fellowship with Jewish Christians. Cornelius lived in Caesarea, the political capital of Judea under Herod and the Romans. (Given that Jerusalem was a holy city to the Jews, it would have been needlessly provocative for the Romans to establish their headquarters there.) Although he is not mentioned again, he and his household presumably formed the nucleus of the Christian community that we find mentioned later (A 8:40; 21:18) in this important city.
O God, who by thy Spirit didst call Cornelius the Centurion to be the first Christian among the Gentiles: Grant to thy Church in every nation a ready mind and will to proclaim thy love to all who turn to thee with unfeigned hope and faith; for the sake of Jesus Christ our Lord, who liveth and reigneth with thee and the Holy Spirit, one God, for ever and ever.
O God, who by your Spirit called Cornelius the Centurion to be the first Christian among the Gentiles: Grant to your Church in every nation a ready mind and will to proclaim your love to all who turn to you with unfeigned hope and faith; for the sake of Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, for ever and ever.