"Then after an interval of fourteen years I went up again to Jerusalem with Barnabas, taking Titus along also. It was because of a revelation that I went up; and I submitted to them the gospel which I preach among the Gentiles, but I did so in private to those who were of reputation, for fear that I might be running, or had run, in vain." (Galatians 2:1-2)It was three years after receiving Christ that Paul went to Jerusalem to meet Peter and James, and it was another fourteen years later before his next trip to meet the rest of the apostles, thus making a total of seventeen years from conversion to his trip to make sure he had not "run in vain." That is a long time. Think back over your own life these past seventeen years. Seventeen years ago I was still living in Las Vegas and my youngest, who is now in college, was just becoming a toddler. For seventeen years Paul preached the Gospel without ever doubting what he taught. All Paul knew was that He has received a revelation from Christ and a commission from God as an Apostle. In that knowledge he did all in his strength to fulfill that commission and to preach that revelation.
So why now? After seventeen years, why now? Luke fills in some of the gaps. "Some men came down from Judea and began teaching the brethren, 'Unless you are circumcised according to the custom of Moses, you cannot be saved.' And when Paul and Barnabas had great dissension and debate with them, the brethren determined that Paul and Barnabas and some others of them should go up to Jerusalem to the apostles and elders concerning this issue." (Acts 15:1-2) Paul went back to settle this issue and to verify that the Gospel he preached was the same Gospel the Apostles in Jerusalem preached.
Paul says he went up "because of revelation" or "according to revelation." It is unclear if he meant that he received a revelation from God to go to Jerusalem or if it was because of the revelation of the Gospel he received that we went to Jerusalem; to compare his revelation to the revelations given to the other Apostles. Either way, he went to "submit" to them the Gospel he preached. The word translated here as "submit" could more literally be translated, "to set forth" or "to declare." Paul did not go to submit his revelation to their judgment and correction, but to declare to them what He had been preaching; to let them know what he had been doing and teaching; to compare notes and to decide how to proceed. Paul was not ready to give up his revelation but he wanted to know how it compared to what the other Apostles were teaching.
In the end, the other Apostles added nothing to Paul's message; the message of salvation by grace was left intact. Even the Greeks who accompanied Paul to Jerusalem were not required to be circumcised according to the law. They were all in agreement and harmony was restored to the church.
Paul's message to the Galatians was that the message they had received had stood the test of time and was confirmed by the revelations received by the other Apostles; they were all in agreement. There was no difference between the Gospel Paul preached and that which was first preached in Jerusalem. In the end, there is only one Gospel regardless of who preaches it and we can trust in that Gospel because it is the message of Christ.