I’ve had this same question. When you consider the Gospel accounts of the apostles, they knew Christ and received training from Him, and Peter was established as the leader and first Pope of Christ’s church. Then along comes Paul, and there seems to be some confusion, although ultimately Paul’s teaching is that he was to go to the Gentiles:
Paul: “For I speak to you Gentiles, inasmuch as I am the apostle of the Gentiles, I magnify mine office…[Rom. 11:13]”
Peter: “Men and brethren, ye know how that a good while ago God made choice among us, that the Gentiles by my mouth should hear the word of the gospel, and believe. [Acts 15:7]”
Paul: “But contrariwise, when they saw that the gospel of the uncircumcision was committed unto me, as the gospel of the circumcision was unto Peter;
(For he that wrought effectually in Peter to the apostleship of the circumcision, the same was mighty in me toward the Gentiles

And when James, Cephas, and John, who seemed to be pillars, perceived the grace that was given unto me, they gave to me and Barnabas the right hands of fellowship; that we should go unto the heathen, and they unto the circumcision.
Only they would that we should remember the poor; the same which I also was forward to do.
But when Peter was come to Antioch, I withstood him to the face, because he was to be blamed. [Gal. 2:7-11]”
And when I read the book of Acts, the narrative of Paul’s activities just takes over and the 12 fade away. Protestants use this constantly to show how Paul was guided in the Spirit, the “apostolic age” ended, and we are in the Spirit-guided age now and the Roman Church is unnecessary, etc. Am I the only one who comes up against this dilemma?