Have you ever thought, "If God ordains all things, then why should I do anything?"?  If so here is a short answer, but a good answer.  Also check out the bibliography mentioned.

http://theologica.blogspot.com/2005/03/divine-sovereignty-and-necessity-of.html

Don Carson gave two messages at Denver Seminary's chapel.  Here they are in mp3 format.

http://www.denverseminary.edu/worship/media.php