A young seminary student went home for Christmas break. A horrible snowstorm stranded the regular minister in another town. The leaders of the congregation asked the young man to substitute for the regular minister.
The young preacher started his sermon by explaining the meaning of a substitute. "If you break a window," he said, "and then place a piece of plywood over the hole -- that's a substitute."
After the sermon, a well-intentioned woman wished to compliment the young man. As she enthusiastically shook his hand, she said: "You were no substitute. You were a real pane!"