This verse is from what is sometimes called the Sermon on the Plain. In this part of the sermon, Jesus tells us how we can judge a person’s character. We do it in much the same way we look at a tree or plant to tell if it is a “good” plant or not: “No good tree bears bad fruit, nor does a bad tree bear good fruit. Each tree is recognized by its own fruit. People do not pick figs from thorn bushes, or grapes from briers” (Luke 6:43–44). If you want to know what kind of tree or plant you have, you have to look at its fruit. A pear tree sounds like a good tree, but, if you have a Bradford pear tree, you will get small, inedible pears about the size of marbles. What is on the inside—what the tree is really “made of”—will determine what kind of fruit it produces. Jesus says that the same is true of people.
In Luke 6:45, Jesus says that people can be judged by what they say and do because these things reveal what is really inside the person: “A good man brings good things out of the good stored up in his heart, and an evil man brings evil things out of the evil stored up in his heart. For the mouth speaks what the heart is full of.” If you want to know what is on the inside of a person, you simply watch his actions; listen to what comes out of his mouth on a regular basis. This is not being judgmental; this is being realistic.
If a person is angry, rude, lewd, or immoral on a regular basis, you can be assured that this is what he is like “on the inside.” If a person is consistently kind, encouraging, and polite, then you can be sure that is what he is like “on the inside.” Of course, it is possible that someone might put up a façade to deceive others regarding his character, but eventually what is inside will come out. The mouth speaks out of the abundance—the overflow—of the heart.
The primary point of application in Jesus’ words seems to be this: when we see evil consistently coming out of a person in word and deed, we should not deceive ourselves by saying, “I think he really is a good person inside; he just has some bad habits” or “That’s just the way he talks, but he’s not really like that.” How many people fall in love and get married, thinking that the bad behavior they have observed is only an aberration? How many parents deceive themselves regarding the spiritual state of their children, thinking that they are true believers because of a childhood profession of faith, even though their lives demonstrate a heart of evil?
When Jesus said, “Out of the abundance of the heart the mouth speaks,” He meant that consistently sinful words and deeds are indicative of a sinful heart. Rather than always giving people “the benefit of the doubt,” we would do well to recognize the “fruit” we observe and respond accordingly. Being a “fruit inspector” does not mean we consider ourselves to be without sin; it does mean that we are realistic about whom to trust and whom we allow to exert influence over us and the people for whom we are responsible.