Verse 1
Four fold - historical argument.
1. Time before Paul’s conversion (see Galatians 1:13 Galatians 2:1)
2) Time Immediately After Conversion v. 15-24
3) Paul Endorsed by Jerusalem Apostles
fourteen years -- After his first visit to Jerusalem after conversion, Acts 9:26-30. (Some commentators, however, suppose that the date of the fourteen years is to be reckoned from his conversion.)
went up again Jerusalem -- The relief of Acts 11:17-30 had been about 7 years earlier. The visit of which Paul now speaks of coincides with Acts 15:1-2 ff.
Paul is not saying that was his next visit, but he is telling of another time he went up to Jerusalem and did meet with the apostles.
The use of again need not mean: for the second time. It does not rule out the possibility of a visit sometime between the occasions indicated in Galatians 1:18 and Galatians 2:1. ... at issue here in Galatians 2:1 is material agreement about a very pressing point: whether the Gentiles are bound by the law of Moses. - Ridderbos
with Barnabas -- Paul’s first ally who vouched for him before the apostles at Jerusalem (Acts 9:27), and became his traveling companion on his first missionary journey (Acts 13:2-3). He accompanied Paul to the Jerusalem meeting, Acts 15:2. (See note on Acts 4:36)
Titus -- Luke, in the Acts of the Apostles Acts 15:2, says, that there were others with Paul and Barnabas on that journey to Jerusalem, but did not mention Titus by name. Titus was a Greek who had been converted to Christ but without being circumcised.
Titus is not mentioned by Luke in the Acts of the Apostles, [this had led some to think Titus may have been a relation to Luke, even his brother possibly] and though his name occurs several times in the Second Epistle to the Corinthians 2 Corinthians 2:13; 2 Corinthians 7:6; 2 Corinthians 8:6, 2 Corinthians 8:16, 2 Corinthians 8:23; 2 Corinthians 12:18, yet it is to be remembered that that Epistle was written a considerable time after this to the Galatians.
Titus was a Greek, and was doubtless converted by the labors of Paul, because he calls him his own “son,” Titus 1:4. He attended Paul frequently in his travels; was employed by him in important services (see 2 Corinthians in the places referred to above); was left by him in Crete to set in order the things that were missing, and to ordain elders there Titus 1:5; subsequently, he went into Dalmatia 2 Timothy 4:10, and is supposed to have returned again to Crete, where it is said he propagated the gospel in the neighboring islands, and died at the age of 94 - (Calmet as a source by Barnes)
Sir William Ramsay and A.T. Robertson speculate that Titus was Luke’s brother, explaining the absence of any specific mention of him, but this is unsubstantiated.