One of the most underrated elements of going to big conferences is the chance to buy books at discounted prices. One of the many books I picked up at the Wheaton Theology Conference was I. Howard Marshall's New Testament Theology: Many Witnesses, One Gospel. I hadn't owned one before and knew that it was a significant gap in my library, but I did not expect it to be as useful as it has been. I can think of at least four very practical ways in which a theology can be used very profitably.
1. As an aid to devotional reading
Are you about to start reading through Mark in your daily devotions? Before you start read the chapter in Mark in your theology. It'll take a little over an hour and it will greatly improve the depth of insight you gain from your devotional time. You'll have a much clearer picture of how the gospel fits together and what the main themes are that Mark was trying to communicate.
2. To provide context before doing Bible study
In our church's small groups were not currently going through any book of the Bible, we're jumping around a bit. This week I'm covering Hebrews 13. I haven't studied Hebrews before so I am a little unfamiliar with it. In about an hour I got an excellent overview that helped me see how the closing exhortations fit into the book as a whole. It will keep me from extracting the text out of its context.
3. As a preparatory step before beginning a major study of a book of the Bible
None of us bring a blank slate to the text. We've probably read the text before and have some sort of preliminary understanding before we commence our study. In addition to reading the introductions to whatever commentaries you are going to use, read the chapter in your theology. It will help come to the text with some pre-understanding that your study will hopefully deepen.
4. As a tool for gauging the quality of your study of a book of the Bible
Don't only read the theology before you begin your study, read it after you finish. Compare the conclusions you drew with those the author of your theology has made. It's ok to disagree, but is your reasoning defensible? Also, is there a theme that you completely missed? If so go back and spend some additional time in the text to make your understanding of the book more complete.
How else have you used them, and what is your favorite New Testament Theology?
I'm also on the lookout for a good Old Testament Theology that takes a book by book approach (many seem to be more thematic). Are there any that you've used that you would recommend?