Motivation

I am motivated to lead a study on spiritual types at our church.  I am motivated to work on my Gospel of Mark assignment.  I am motivated to work on my Mission of the Church assignment. I am motivated to do my yard work and house keeping.  Sounds good doesn't it.  The problem is the next assignment due is Humanity, Sin and Grace and I am not motivated to work on that.  Procrastination has set in and I would rather work on all those other things.  I am happy that other things are getting done but soon, very soon, I am going to have to come up with about 3000 words assessing an academic's arguments on humanity and God for coherence.  They were coherent, now where to the other words come from?  Why am I happy to engage in the lectures, reading and topic but not the assignment?  Why is this the only subject, that I am not motivated to finish? Motivation seems to be as slippery topic as say, well, grace (update) that is understanding grace.