Here Jesus explains what he means by the parables. Whoever is not a follower of Jesus—does not know dependence on him—cannot possibly mean something to a fellow human being that is really good. If you are truly delighted with the grace of God in Jesus Christ, only then will your speech be rich for others. If your heart is a richly filled treasury, your mouth will overflow with that richness. For preachers of the gospel, this verse is a cause for self-examination. The question needs to be asked, Am I full of God’s goodness?
Only when the heart is full of it does something good come out of the mouth.
45 The good person out of the good treasure of his heart produces good, and the evil person out of his evil treasure produces evil, for out of the abundance of the heart his mouth speaks.