Why did the apostles add nothing to Paul at the Jerusalem conference?
The apostles added nothing to Paul at the Jerusalem conference because they recognized the gospel of the uncircumcision had been committed directly to him, and they lacked the same revelations. They saw God working mightily through Paul to the Gentiles, just as through Peter to the Jews, so they had nothing to contribute.
Les explains that the twelve were still unaware God was turning to the Gentiles and that Israel would soon lose the Temple, priesthood, city, and nation. They thought they were still in control. Paul said that whatever they seemed to be made no matter to him, for God accepts no man's person. When they added two and two, they could not add anything to what Paul knew, because they did not have near the revelations he had. In conference they added nothing to him. Yet contrarywise, Paul had much to tell them they had never heard. When they saw the gospel of the uncircumcision was committed to Paul as the gospel of the circumcision was committed to Peter, they understood these were two separate entities. The same God who wrought effectually in Peter to the apostleship of the circumcision was mighty in Paul to the Gentiles.