It's not necessary for every homily in Mass to start with a joke. But sometimes it helps. One of the deacons at our parish began his homily with this story that he said he'd heard recently.
A woman had two sons, one in first grade, and the other in the third grade. She made pancakes for breakfast on a Saturday morning. She ended up with an odd number of pancakes, and both of her sons were whining that they wanted the last pancake.
The mother saw this as an opportunity for some spiritual learning. So she explained to them how Jesus would have reacted in this situation. She said that as an act of sacrifice and love, Jesus would have let his brother have the last pancake.
After hearing this story, the older boy turned to his brother and said, "Okay, you be Jesus so I can have the last pancake!"