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. – Luke 6:45
Jesus was saying this, at least in part, to expose the hypocrisy of the human heart. This verse is in connection with the speck and plank illustration just a few verses before. The main concern here is the heart. If you bring someone’s sin to light with the wrong heart, you are a hypocrite. And what comes out of your mouth flows out from your heart.
This is a principle that extends beyond addressing people’s sin. This principle is true in any situation: out of the abundance of the heart his mouth speaks. What’s coming out of your mouth? Is it praise or complaining? Is it holiness or profanity? Is it love or animosity? Whatever the case is, it is coming from the heart. It will do one no good to change the way he speaks if his heart does not change also.
God, change our hearts, that what comes out of our mouths is pleasing to Your ears.