“Part of the point of the doctrine of the trinity is that when we say ‘Father, Son and Spirit’ this doesn’t have the effect of having a q.e.d at the bottom. It isn’t ‘Father, Son and Holy Spirit – there you are, told you so. That’s all you need to know, put it in your back pocket and you’ve got God on tap.’ But rather the very fact of talking trinitarianly is a way of saying, ‘Here is mystery, which you’re going to have to live into. Here is mystery, which each generation will have to re-appropriate for itself. Here is something that you cannot possess, because if it’s true, it possesses you.’ That’s very hard for so many Christians to take, both so-called radicals and so-called conservatives.”
–N.T. Wright, Thinking about God in Tommorrow’s World lecture, June 15, 2007
Christianity Tomorrow 
And mystery certainly doesn’t stop there. 🙂