There was no question about whether the gospel should be preached to the Gentiles; Peter had been shown this personally by the Lord (Acts 10). The key unresolved issue was, what Jewish practices should the Gentiles be required to follow? There were two ways of looking at this, and even though Paul was quite clear about the issue, he knew that his enemies were bound to confuse matters.
There are times when an issue needs to be talked through among a limited number of responsible leaders before it is made public. This was not a question of putting on a show of unity, but of genuinely reaching agreement. Appearances are important, and if there was any misunderstanding here, it had to be sorted out before the issue was brought before the whole church or else the disagreement between the leaders could be magnified as further fractures occurred along the lines of misunderstanding among ordinary church members. This was not a political move but one designed to arrive at the truth before teaching the church as a whole.
Why does Paul say that he was sent by revelation when Acts 15:2 says they were sent by the Antioch church? The two statements do not contradict each other. The Spirit of God who spoke to Paul works in harmony with the church. Paul may have been unsure whether or not he should go to Jerusalem, because, in submitting his gospel to the other apostles for their approval, he was in danger of giving the impression that he was unsure of his doctrine and apostolic authority. God therefore made his will clear.