I tend to underestimate the power of repetition.  Repetition can be a useful rhetorical device in a sermon, I often try to come up with a key phrase that summarizes the point of the sermon and repeat it several times in the course of a message. 

But what I am sometimes tempted to neglect is repeating concepts that I have taught in previous sermons.  So, for a random example, last week I was preaching on Deuteronomy 18:15 and the promise of a prophet like Moses.  In the course of the message we looked at the Transfiguration and the significance it has in showing the fulfillment of the prophecy in Deuteronomy. 

Well, in Luke 9:31 we are told that during the Transfiguration Moses spoke to Jesus about his coming departure (Greek: exodos).  All commentators agree that it's significant that Luke chose to use that particular word, but I wasn't sure whether it was something I ought to mention in the context of my sermon on Deuteronomy 18:15.  But as I deliberated the issue the thought occurred to me, "I don't really need to point this out.  After all, I mentioned this when I preached on Luke 9 three years ago." 

As an experiment, I asked five people in my church who would have heard that sermon three years ago if they remembered the significance of Luke's word choice there in 9:31.  All of them remembered the sermon, but none of them remembered why the word in that verse mattered.

The take-away?  I need to be remember to be realistic about what people are retaining from the messages I preach each week.  I also need to embrace repetition.  Just because I've said it a bunch of times doesn't mean everyone in the congregation has heard it.  And that reminds me to keep preaching and repeating the same gospel week in and week out.