How about our Paladin, Joseph, screwed up in the recent past and he's on a quest to regain his honour.  Maybe there's a legendary beast or specific item belonging to your church that needs recovering.  Maybe he has a loved one who is I'll and can only be saved by powerful magic. 

The important thing is that he desperately needs to acquire this thing or to do this thing.


This is where you depend on your GM to include whatever that thing is.