While I believe in the importance of illustrations, I do not believe that 50 percent of a sermon must be applications. If I preach that we should love our neighbors, I need not devote half of my sermon to telling my people in exhaustive detail how to love this way. It is the Spirit who applies the truths of Scripture to each person. But if we fail to give our hearers some clear principles they can apply, we have failed to present God's Word properly. Remember, people live out their theology or beliefs, but they forget your exhortations. They will apply what they genuinely believe to be true.

source: John MacArthur, http://www.biblebb.com/files/macqa/IA-sermonapp.htm tags: Preaching