Verse 2: And I went up by revelation, and communicated unto them that gospel which I preach among the Gentiles, but privately to them which were of reputation, lest by any means I should run, or had run, in vain. Note that he went up by revelation to Jerusalem. Luke also mentioned this in Acts 15:2 when he wrote, When therefore Paul and Barnabas had no small dissension and disputation with them, they determined that Paul and Barnabas, and certain other of them, should go up to Jerusalem unto the apostles and elders about this question.
So, the question is, did God tell him to go or did the assembly at Antioch tell him to go? The issue is the wording of the King James. I believe that it means that the church at Antioch did send him, but the subject was to be the revelation of the mystery that he had received. This, of course, will be the first time that he is going to share the mystery with the Twelve. It was there that he first shared the that gospel which I preach among the Gentiles.
This is the first time in the Bible that we see that Paul's gospel that he preached go the Gentiles was different than the gospel that Peter continued to preach to the Jews. Bear in mind that this counsel occurred 19 years after Pentecost! I stand amazed at how many in the Body of Christ refuse to recognize that these two gospels were different. Think about it, why would Paul take the time to visit the Twelve if they were teaching the same thing? Theirs was still the kingdom gospel which was under Law. Paul's was the new grace gospel which was apart from the Law.
Them which were of reputation is a reference to the Twelve. Notice also that he met privately with them. No doubt, this was to avoid a riot in the city.
The final part of the verse says lest by any means I should run, or had run, in vain. In other words, lest my labors be in vain or lost. He wanted to make sure that they were in agreement as to what each was doing and teaching lest they clash due to misunderstanding later. He didn't want his work to be undone with confusion.
Albert Barnes says it this way, "Lest the effects of my labors and journeys should be lost." Barnes goes on to say that "Paul feared that if he did not take this method of laying the case before them privately, they would not understand it. Others might misrepresent him, or their prejudices might be excited, and when the case came before the assembled apostles and elders, a decision might be adopted which would go to prove that he had been entirely wrong in his views, or which would lead those whom he had taught, to believe that he was, and which would greatly hinder and embarrass him in his future movements."
Verse 3: But neither Titus, who was with me, being a Greek, was compelled to be circumcised: This verse is parenthetical in that it is a reference back to Acts 15:1 when those from Judaea taught the brethren, and said, Except ye be circumcised after the manner of Moses, ye cannot be saved. Obviously, Paul was teaching that it was not necessary, or he would not have made the point.Verse 4: And that because of false brethren unawares brought in, who came in privily to spy out our liberty which we have in Christ Jesus, that they might bring us into bondage: The false brethren are the ones that brought the message in Acts 15:1 that the Gentiles needed to submit to the law of circumcision to be saved thus bringing them into bondage. They, unlike many in the church today, realized that Paul's message was different than that of the Twelve.
Paul will go on to say in Galatians 5:1-5, Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage. Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing. For I testify again to every man that is circumcised, that he is a debtor to do the whole law. Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace. For we through the Spirit wait for the hope of righteousness by faith. Unlike what the Seventh Day Adventists and many others today, you either keep the whole law or no law. Finally, the fact that he refers to them as false brethren implies a bit of chicanery. In other words, they had infiltrated the group first and then sought to correct them. They were not there to be a part of the fellowship, but to spy it out (cf. the Greek).