Paul Had Then Met Peter and Much Later Conferred With The Leading Apostles To Ensure That What He Preached Was in Accordance with What They Taught (Galatians 1:18 to Galatians 2:3).
‘Then after three years I went up to Jerusalem to visit Cephas, and stayed with him for fifteen days. And I saw no other of the Apostles, but I did see James, the Lord's brother.'
Paul is still concerned that they recognise that he was not just a humanly taught man, or a man under instruction from anyone but God. Yet he does not want them to see him as independent of Jesus' chosen Apostles. To him the oneness of the church was all important. It was that that the Lord's Supper testified to (1 Corinthians 10:16-17). Thus he mentions this visit which followed his period of preaching in Damascus, while stressing that during it he only conversed with Peter, and that over a period of a mere fifteen days, and with James the Lord's brother.
‘Then after three years.' Presumably three years after his conversion (although ‘three years' may signify two part years with a full year in between, thus one and a half to two years. Compare how Jesus rose ‘three days' after His death, that is ‘on the third day'). This included his Damascene ministry as well as his period in Arabia (Acts 9:19-25).
‘I went up to Jerusalem to visit Cephas.' This is probably the visit mentioned in Acts 9:26-30). If so the reference to ‘the Apostles' there must signify ‘the Apostolate as represented by Peter' and possibly James the Lord's brother, although James is not necessarily said to be an Apostle. ‘To visit' ('istoreo) means strictly ‘to visit with a view to getting to know' someone. Thus Paul is stressing his intention to become known to Peter while not suggesting that he had anything to learn from him. It was not surprising that Paul wanted to meet the leader of the band who had been specially set apart by Jesus, and to share fellowship with him and learn something of the life of Jesus from a disciple's point of view. This last is emphasised by the fact that he also mentions ‘James, the Lord's brother' (always elsewhere simply called James), who obviously knew Jesus like no one else did. He had been His younger brother, His ‘kid brother'.
‘And I saw no other Apostles but I did see James, the Lord's brother.' Presumably the other Apostles were absent from Jerusalem. James, the Lord's brother saw the risen Jesus (1 Corinthians 15:7), united with the Apostles prior to Pentecost (Acts 1:14), and was prominent in the Jerusalem church (Acts 12:17; Acts 15:13), after the death of James the Apostle, the brother of John (Acts 12:2). It is possible that he was seen as replacing James among the twelve, although it is never so stated. But he was certainly a rock in Jerusalem until he was martyred by stoning around 62 AD in an interregnum period for Roman procurators.