The worst sermon I ever preached was in Canajoharie, New York, the chewing-gum capital of the world, where I was invited to address what was described to me as an ailing congregation.

The Gospel lesson for that Trinity Sunday was John's story about Nicodemus's search for new birth. It was a promising sign, I thought, and proceeded to construct an eight-page masterpiece on faith and doubt. Sunday morning arrived, the processional hymn began, and I marched into a church with three people in it—five, including me and my host.

Two were elderly women, still weepy over the loss of a friend the day before. The third was a heavy, angry-looking man who occupied the other side of the church all by himself. When the time came for the sermon, I crept into the pulpit, wondering what to do. I tried the first page of my manuscript and abandoned it; it was like reciting poetry to a wall. With a fast prayer to the Holy Spirit, I put my notes away and tried to summarize what I had planned to say. The ...