Over the last 9 1/2 years we've taught 23 books of the Bible (it'll be 24 once I finish Esther in February). If you know me, then you know one of my life goals is to teach through the entire Bible. I'm sure there a few that I'll teach more than once, but my goal is to teach the 'whole counsel of God'. 

Having said that, why would I want to teach through the entire Bible? Here's a few reasons: 

1. It's the primary way to disciple new believers.

2. It teaches people to work their way through the Bible personally

3. You deal with topics you'd never talk about only doing topical messages

4. It lowers the stress level of the Pastor because he always knows what's coming next and doesn't hae to stress out about what to teach.

5. You will always come back to the Bible's major themes. 

There's other reasons, but I'll leave it at that.

I would encourage you to build book studies into your preaching calendar. You'll see a difference in your congregation!