If you have to explain a joke it isn't funny. It takes more than the right combination of words to create humor. Physical movement, facial expression, voice inflection, all contribute to humor. Some jokes, if only read from a page, simply miss the mark. This parable suffers that fate.
This parable will teach a lesson in a Bible class. The analogy clearly transfers. Jesus, the small seed, begins a Kingdom movement that grows to fill the whole earth. The idea isn't new. Many Kingdom builders began with a small militia, grew an army and established empires. Mark wants us to understand Jesus' Kingdom differs from those empires.

The Kingdom of Heaven grows contrary to the natural order. It surprises you. We repeat the story about our little league team that won the championship against all odds. An Olympic skater amazes us when she gives a medal winning performance through overwhelming grief. The room falls silent when a child offers a simple but profound answer to a question the adults have been discussing at length. The Kingdom of Heaven grows like this.
You may write something in response to this blog, that dramatically changes the course of someone's life. The Kingdom of Heaven grows like this.