When Jesus was about to leave this earth, ascending back into Glory (3rd Heaven) He told the remaining apostles that He had many things to tell them, but they were not able to accept, comprehend, discern, them yet.
Later, from Heaven Jesus called Paul and sent Him as "the Apostle to the Gentiles", and personally gave Paul the revelation of the "Gospel of the Grace of God", and the other revelations.. that are "Paul's doctrine".
In Acts 15... Paul met all the Apostles and explained the "there are many things i have to say to you", revelations that Jesus didnt give them.
And these revelations, are what we are to understand as "Paul's Doctrine", which is THE = "doctrine for the Church".
And this is why Paul wrote most of the NT epistles., as its in Paul's doctrine that we find the fullness of the Revelations, that Jesus offers His "body." so that they can mature spiritually, by revelation knowledgge .......that you find within Paul's doctrine, as you study it, over time... with discipline.
A mistalke that 95% of Christians make, is that they try to "do Christianity"....... vs "receive the knowledge of God" that becomes their spiritual depth and perfecting of their discipleship.