During the Middle Ages there was a popular story which circulated about Martin of Tours, for whom Martin Luther was named. It was said that Satan once appeared to St Martin in the guise of the Savior himself saying that he was Jesus.
Martin was ready to fall to his feet and worship this resplendent being of glory and light. Then, suddenly, he looked up into the palms of his hands and asked a penetrating question, "Where are the nail prints in your hands?"
With that question, the strange visitor vanished out of sight.
- Sermon Illustrations