Though the Greek text simply says that Paul went to Jerusalem again
without specifying the number of previous visits,1 the fact that Paul is defending the divine origin of his gospel suggests that it must have been his second visit.2 If he failed to mention one of his visits to the city, that would give credence to the accusations of the Judaizers who claimed that he learned his gospel from the Jerusalem apostles and then distorted it over time.3 Travelling with Barnabas, he likely made the trip from Antioch (Acts 11:25–26) in response to the prophecy of Agabus (Acts 11:27–30).4
1 Then after fourteen years I went up again to Jerusalem with Barnabas, taking Titus along with me.