I read the blog, Cognitive Daily, and today stumbled into something worth remembering.  The piece was on the effectiveness of humor in Super Bowl advertising, but speaks to preaching as well.

Surprisingly, there actually hasn’t been much research on the effectiveness of humor in ads. Instead, most research has focused on expectancy: if something in an ad is unexpected, it’s more likely to be remembered than something we expect. Even more importantly for advertisers, the unexpected event in the ad must be directly related to their product. (Source)

So, we need to surprise and need to surprise on point.