‘Then after a period of fourteen years I went up again to Jerusalem with Barnabas, taking Titus also.'
Having established that he was not dependent on either the Apostles or the Judean church for his authority or his teaching he now wants to stress that nevertheless, when finally his teaching was discussed with the Apostles they were totally satisfied with what he taught. This may be the visit in Acts 11:30 with Acts 12:25, or the visit in Acts 15 which resulted in the Apostles and the church leaders in Jerusalem pronouncing on the question of what was to be required of Gentile converts to Christ and whether the circumcision of Gentile converts was necessary or required (Acts 15:1-29). ‘Again' (palin) does not necessarily mean ‘a second time' only ‘another time', and the mention of this visit here does not necessarily suggest that there were no visits in between. It is mentioned because it was then that Paul and the Apostles had a full discussion on doctrine resulting in their complete agreement on major issues.
Either way, as it was ‘fourteen years' after he had started preaching it could not be cited as the source of his basic message, for he has already established that his doctrine was received from God by revelation long before that time.
‘Taking Titus also.' The importance of Titus on this occasion was that he was Gentile through and through with no Jewish connections and the question of whether he should be circumcised would therefore be a crucial one. Titus is never mentioned anywhere in Acts. By the time Acts was written Titus' situation was no longer relevant.