What does St. Paul think of the Church?

Quite a bit, it seems. He had previously talked about how salvation is by grace alone though faith, then in his letter to the Ephesians in Chapter 3, he reminds his reader of the grace that was entrusted to him -- a grace meant for the Ephesians. Why does God need to go through a man (and Paul considers himself the least of the saints)? Furthermore, he goes on about the mystery of salvation in Christ was kept hidden until it could be revealed though the Church. Again, why through the Church?
   My take on this is that we often take for granted what "church" is about, but we must see, from the rather Catholic perspective of St. Paul, in that chapter and elsewhere,that there is more mystery in the Church than seems obvious to any who scoff at the idea of "one, holy, catholic and apostolic Church" and prefer the term "assembly" or "congregation." God chose to reveal the mysteries of his grace through the Church on so many levels, and to dismiss the notion is to miss out on profound revelations that, apparently, are front and center.