1 Then after fourteen years, I went up again to Jerusalem, this time with Barnabas. I took Titus along also. 2 I went in response to a revelation and, meeting privately with those esteemed as leaders, I set before them the gospel that I preach among the Gentiles. I wanted to be sure I was not running and had not been running my race in vain. 3 Yet not even Titus, who was with me, was compelled to be circumcised, even though he was a Greek. 4 This matter arose because some false believers had infiltrated our ranks to spy on the freedom we have in Christ Jesus and to make us slaves. 5 We did not give in to them for a moment, so that the truth of the gospel might remain with you.
6 As for those who were held in high esteem—whatever they were makes no difference to me; God does not show favoritism—they added nothing to my message. 7 On the contrary, they saw that I had been entrusted with the task of preaching the gospel to the Gentiles, just as Peter had been to the Jews. 8 For God, who was at work in Peter as an apostle to the Jews, was also at work in me as an apostle to the Gentiles. 9 James, Cephas and John, those esteemed as pillars, gave me and Barnabas the right hand of fellowship when they recognized the grace given to me. They agreed that we should go to the Gentiles, and they to the Jews. 10 All they asked was that we should continue to remember the poor, the very thing I had been eager to do all along. (TNIV)
Paul continues to tell his readers about his past in defense of his gospel. Here we read of another trip to Jerusalem after fourteen years . Paul went up to Jerusalem with Barnabas and Titus, one a Jew and the other an uncircumcised Gentile. All three of them were united in one party under the same gospel. As Hays notes, the delegation's composition bore witness to the gospel in and of itself. Jew and Gentile were united into one new man (Eph. 2:15).
Somehow, in a revelatory manner, God had told Paul to go up to Jerusalem. Apparently it had been revealed to Paul that God wanted the leaders of the Antiochene mission to the Gentiles and the leaders of the Jerusalem church to have a conference discussing the incorporation of Gentile Christians into the church. Did they need to be circumcised? So, Paul went and met with the leaders of the church in Jerusalem to lay out his gospel. Since unity of Jews and Gentiles in Christ was one of the goals of Paul's gospel, it was very important that he be able to achieve that. If the Jerusalem church disagreed with Paul and forced a split in the church, then Paul would have been running his race, to bring that unity, in vain. When we understand Paul's goals thus, it makes it clear that he wasn't telling the Galatians that he went to get his gospel the stamp of approval from the Jerusalem church.
Verses 3-5 give us a hint at why he went and why he brought Titus. Titus was brought along to show the fruit of the circumcision free gospel. The Holy Spirit had worked powerfully in Titus, and he became one of Paul's most trusted co-workers. In the face of such evidence, how could anyone claim that circumcision was necessary for entering into the people of God? Paul went up to Jerusalem because he had faced opposition to his gospel, and to attempt to satisfy his detractors and deal with the issue of circumcision once and for all.
Verses 6-9 continue to show that Paul considered compulsory circumcision of Gentiles to be a dead issue. The Jerusalem apostles did not require Paul to have his converts circumcised. They ratified Paul's gospel as being the true gospel and gave him the charge to continue preaching to the Gentiles. Thus by mentioning this agreement, Paul is firing across the bow of the Teachers. They are intruding on his territory and it is they, not he, who are at odds with the agreement he made with the Jerusalem apostles. Case closed.
One thing that sticks out as odd at first glance is the exhortation to remember the poor. Why would the apostles command that of Paul? Clearly, as Acts 11:27-30 shows, Paul had been faithful. While it's hard to ascertain why, I would conjecture that it was out of a desire to show that Jews and Gentiles truly were one. What better way for the uncircumcised Gentile Christians to show their love for their circumcised Jewish brothers than by sacrificing of themselves for those in need. The collection provided an opportunity for a beautiful display of the love and unity that comes through being united in Christ.
 Commentators are split on whether Paul means fourteen years from the last trip to Jerusalem or fourteen years from his conversion. I will address this issue in a later post on the chronology of Galatians and Acts.