Exegetical vs. Topical Preaching

There are most basically two types of sermon, which I found described quite well today by a Black minister friend:

• a minister finds an idea, then goes to Scripture for texts that match it, or
• a minister finds a Scripture, then goes to the world for ideas that match it. 

My friend claims that this is why Churches in Africa are susceptible to strange teachings and strange emphases -- their teaching is topical, not exegetical. OBSERVATION: I personally have sought to preach one topical sermon for every three exegetical sermons. I prefer exegetical preaching, because it obliges one to preach on certain subjects, and is comprehensive rather than selective.