Too many Christian preachers don’t know enough about (or make a practice of) expository preaching. Don Carson gives six reasons to not abandon or, if you have never done it, to start expository preaching:

1. It is the method least likely to stray from Scripture
2. It teaches people how to read their Bibles
3. It gives confidence to the preacher and authorizes the sermon
4. It meets the need for relevance without letting the clamor for relevance dictate the message
5. It forces the preacher to handle the tough questions
6. It enables the preacher to expound systematically the whole counsel of God

Some of these points are not immediately obvious from their brief titles but at 564 words it’s a quick read to get the deeper details.

http://thegospelcoalition.org/blogs/tgc/2013/11/06/6-reasons-not-to-abandon-expository-preaching/