…famous verses about God’s Word being “like fire…and like a hammer that breaks a rock in pieces” (Jeremiah 23:29) are not mere rhetoric. I have seen hundreds of specific cases in which the Bible itself contained a power to penetrate people’s spiritual indifference and defenses in a way that went far beyond my powers of public speaking. A handful of times I have even had conversations with angry people who were sure that one of their friends had told me about them and that I had singled them out in the sermon. I was able to swear honestly that I had had no idea at all about their issue—that it was the Bible itself exercising its power to lay bare the “secrets of their hearts” (1 Corinthians 14:25). I don’t enjoy angry listeners, but I must say I love those conversations.
—Timothy Keller in Preaching: Communicating Faith in an Age of Skepticism