Paul identifies three "pillars" of the early church James (Jesus' brother), John, Peter kjv@Galatians:2:9. Modern Catholics identify only one: Peter. It is James here that delivers the group's verdict. John is either silent or absent. Paul is portrayed once again as serving the church under their authority (even when he has disagreement). I have no doubt that the Spirit was sought for this momentous decision but is not quoted. There is plenty of OT text regarding the inclusion of gentiles, but not mandatory circumcision of them. The decision is based then upon the consistency of the doctrine of saving grace.
There is no doubt that the doctrine of Grace is hard to understand down to it's deepest core, even by those of the early church and by Apostles that should have known better. The mind naturally wants to flip it around to do works towards justification. Our works fall short each and every time, even our best works. They are certainly not payment for sin and reconciliation. Christ's death would be in vain otherwise.
Peter received correction. Had he been the first Pope and had the Pope been given immutable divine interpretation as supposed by Roman Catholic doctrine, he would not have needed correction. Paul would have shamefully exceeded his lesser authority. Their doctrine follows from a possible misinterpretation on the proclamation Jesus made that on 'this Rock' He would build His church. Rock more likely meaning the divinely revealed faith and not just Cephas 'the rock' personally kjv@Matthew:16:17-20 (literally - You are 'piece of rock' and upon this 'massive Rock' (which flesh and blood have not revealed) I build my church).
2012 - pBiblx2 Field Wise Bible System Version 2.0.9d - GPL3