The Trinity is a concept that is difficult for all of us to really understand. The following is an answer someone gave on a post I liked and the link below it will show the entire discussion with other opinions:
One answer to this is that the Holy Spirit proceeds forth from both the Father and the Son (I think that's the Eastern Orthodox's position, in contraposition to Roman Catholicism). If that's the case, then as long as the Second Person of the Trinity is incarnate, the Holy Spirit could only proceed forth to humanity also incarnated
as far as Paul's teachings, first I definitely believe he was put in the position of authority by God and what he teaches is God inspired, I also believe a lot of his humanity shows in his writings that may not be part of what is absolute Truth. Some of what he writes seems to be a matter of cultural practicality of the time in history.
I just have a hard time with a few things he teaches...