I'd also recommend Kuyper's work on it, which is probably the most extensive. It was just republished in a paperback version. R.C. Sproul has a book on it which is even more basic. So, I'd read them all in this order: Sproul, Ferguson (which is indeed outstanding), Kuyper, Owen.

__________________
Rev. Lane Keister
Teaching Elder, PCA, North Dakota (working out of bounds in a CRC and an RCA church)
http://greenbaggins.wordpress.com
http://brahmsgreenglove.blogspot.com
http://accenttranslation.blogspot.com
Click to get: Board Rules -- Signature Requirements -- Suggestions?