In my church we're now preaching John chs. 14-17. Personally, I am immersed in Trinity studies and, BTW, in the Triune God himself.
Here is a very good resource for serious, historical Trinity-studies: Trinities - theories about the father, son, and holy spirit. It's put together by four very good scholars - three who did Ph.Ds at Oxford, the fourth did his Ph.D at Brown.
One of them, Dale Tuggy, has written the essay on "Trinity" in the Stanford Encyclopedia of Philosophy. This is the essay to read if you want to begin studying the doctrine of the Trinity. After you've read "The Shack," go here.
