The good man, out of the good treasure of his heart, brings forth good; and the wicked [man] out of the wicked, brings forth what is wicked for out of the abundance of the heart his mouth speaks.
The verse closes the Lord's picture of the tree and its fruit with a rule about speech. It raises the sharpest question of the passage: not how a person talks, but what kind of person is talking.
A Question of Nature
The Lord is not measuring behaviour here. He is exposing what a person is. One writer notes how Luke sharpens the wording:
Then He shows plainly that it is a question of nature. "For no good tree bears bad fruit, nor again does a bad tree bear good fruit." You cannot change the nature. … "Each tree is known by its own fruit." This is unique to Luke — I mean the way Luke states it so strongly. Matthew says, "You will recognize them by their fruits." Luke makes it wider and stronger.
Nature stays hidden, so fruit is how we read it. Here that test falls on people who claim to follow Jesus:
From verse 43 the Lord looks at the outward profession of discipleship. He may have had someone like Judas in view as He spoke. Among those who took the place of being His disciples there might be "an evil man" as well as "a good man." Their fruits show which they are, in both speech and action. Fruit reveals nature. We cannot see into the hidden nature of a tree or a man, but the fruit tells us what it is, easily and correctly.
Where the Good Treasure Comes From
So where does a good store in the heart come from? One commentator traces it to grace, not to anything people own by nature:
In these verses the Lord strikes at people's pretence of goodness while their hearts stay untouched by His grace. They are not born again, so they are still under sin. A good person is one whose heart is purified by faith in the Son of God, for by nature "no one does good, not even one" (Rom. 3:12). Only the grace of God can make a difference in the person. In this case God plants a "good treasure" in his heart. It is the treasure of the knowledge of the glory of God in the face of Jesus Christ, given to "jars of clay" (2 Cor. 4:6-7). Only good can come from this, however weak the vessel may be. Without this good treasure a person has only "an evil treasure" in his heart, and his mouth soon expresses it, for whatever fills the heart most is what the mouth will speak.
A Test for Our Own Souls
The saying also turns back on the listener. Luke's version, one writer observes, is a rule for self-examination:
But Luke presents the matter far more as a moral principle. It is true of every man that out of the abundance of the heart his mouth speaks. This is an important test for the state of our souls. Our lips betray the condition of our heart — of our affections.
A front held in public cannot last:
What is really filling my heart will come off my tongue. And therefore you can always tell what my heart is occupied with, because I have a tongue. I cannot long deceive you.
The Word That Slips Out
It is rarely a speech that exposes us. One writer points to a single word:
The evil is not the things themselves dug out of the earth, but the love in the heart for them. "Out of the abundance of the heart the mouth speaks." An impatient word betrays the heart. A blow I may restrain and yet utter the word.
Guarding the Source
So the cure works at the source, not at the lips:
"And these words that I command you today shall be on your heart" — at the very source of all the issues of life. This is very precious. Whatever is in the heart comes out through the lips, and in the life. How important then, to have the heart full of the word of God! It should be so full that we have no room for the vanities and follies of this present evil world… So we can judge what is in the heart by what comes out of the mouth. The tongue is the organ of the heart — the organ of the man… the heart is the mainspring of our entire moral condition.
Summary
- Nature — The tree decides the fruit. Luke states it in the strongest form: each tree is known by its own fruit. The question is what a person is, not what they do.
- Treasure — By nature no one is good. Grace plants the good store in the heart. Without it, only an evil treasure is there to draw on.
- Mouth — Whatever fills the heart most reaches the tongue. Words are where the hidden store becomes public.
- Test — Luke makes this a test for our own souls. Our lips betray our affections, and one impatient word is enough.
- Source — The heart is the mainspring. So fill it with God's word, until there is no room for the follies of this world.