Thēsauros and Perisseuma, the storeroom and the overflow.

How do I actually tell what is in my heart?

The Lord Jesus answers this directly, and the answer is simpler and more uncomfortable than most people expect.

Listen to what you say.

A good man out of the good treasure of his heart bringeth forth that which is good; and an evil man out of the evil treasure of his heart bringeth forth that which is evil: for of the abundance of the heart his mouth speaketh.

Luke 6:45 KJV

Three Greek words carry the whole thing.

The three words

Thēsauros, translated "treasure", is not a chest of gold. It is a storeroom. A treasury. A place where things are deposited and kept. The heart is being described as a room with stock in it, and whatever was put in is what will come out.

Perisseuma, translated "abundance", means overflow. Surplus. What exceeds the container. This is the key one. The mouth does not speak from what you deposited. It speaks from what has spilled over the top. Which is why you do not choose it, and why it is honest.

Lalei, "speaketh", is in the tense Greek uses for continuous action. The mouth is habitually speaking out of the overflow. Not one slip, not one bad day. The settled pattern of how a person talks.

Put together: the storeroom fills, and once it is full it spills, continuously. What spills is the fruit.

Where you see it

The word "for" at the start of that last clause is doing real work. In Greek it is a causal connector, meaning this is the reason the whole image works. The Lord Jesus has just spent two verses on trees and fruit, and rather than leaving the picture open He anchors it to one thing: the mouth.

That matters because a teacher's own explanation of His own metaphor carries more weight than any application attached to it later. He did not say the fruit is your activity. He said the fruit is what you say.

Matthew records the same teaching and removes any doubt about it.

O generation of vipers, how can ye, being evil, speak good things? for out of the abundance of the heart the mouth speaketh.

Matthew 12:34 KJV

And then He takes it further in the same passage, saying that people will give account for every idle word, and that by your words you will be justified and by your words condemned. Two Gospels, same teaching, same landing place.

Then Paul gives the instruction that follows from it.

Let the word of Christ dwell in you richly.

Colossians 3:16 KJV

Richly means abundantly. Fill the storeroom, and the overflow changes on its own.

What changes

This gives you a diagnostic you can run today, which is the whole point of it.

Audit your habitual speech, not your Sunday speech. The unguarded kind. What came out of you in the last hour, in traffic, in a group chat, when you were tired. Deliberate speech tells you what you want to be. Overflow tells you what you are.

Trace it back to the storeroom. Whatever is spilling was deposited. Not by accident, and usually not recently. If what comes out of you under pressure is complaint, or cynicism, or fear, something has been getting stored.

Change the deposit if you want the overflow to change. This is the only way it works. You cannot manage the overflow at the mouth. People try, and it holds for a while in controlled settings and fails the moment they are stretched. The repair is further back.

Works follow. Speech is the nearest overflow of the heart, so it shows up first. What a person says consistently sets the direction of what they will eventually do. Words are a real-time indicator. Works are a lagging one. That is why the Lord Jesus put the diagnostic on the mouth. You can check it any moment of any day.

So the question underneath the whole passage is not what are you doing. It is what are you saying, when no one has given you a reason to perform.

For your own study

What have I actually been saying this week, when I was not thinking about it?
What does that suggest has been getting deposited?
Where am I managing my speech in public while the storeroom stays the same?
What am I putting into the storeroom daily, on purpose?
If my words set the direction of my works, where are my current words pointing?

Go deeper

The full argument behind this study, including why the passage is commonly misapplied.

The hermeneutical principle

The law of "the first" applies here. When the Master gives His own explanation of His own metaphor, that explanation carries interpretive priority over any application attached later. The Lord Jesus does not leave the tree and fruit image as a bare parable. He closes it with an explicit anchor: the mouth.

The Greek connective gar ("for") is causal and explanatory. That final line is not one more observation added to the pile. It is the reason the whole preceding image works. Everything just said about trees, fruit, thorns, brambles and treasures of the heart is now anchored in one specific manifestation: speech.

The passage does not begin with the mouth. It ends with the mouth. And where a teacher lands is what the teacher meant.

Why Luke's version differs from Matthew's

There are two tree and fruit teachings in the Gospels, and their contexts are not the same.

Matthew 7:15-20 sits inside a warning about false prophets. Matthew's context is discernment of teachers by outward manifestation, and Matthew's version does not include the mouth line.

Luke 6:43-45 sits in a completely different cluster. Around it: not judging (v.37-38), the blind leading the blind (v.39), the mote and the beam (v.41-42, itself about speaking correction to another), the tree and the fruit climaxing in speech (v.43-45), "why call ye me, Lord, Lord, and do not the things which I say?" (v.46), and the two builders who differ in whether they hear and do His sayings (v.47-49).

Luke's whole cluster is saturated with speech: judging speech, correcting speech, confession of lordship, and hearing and doing sayings. The tree and fruit teaching in Luke is deliberately placed inside a speech-oriented framework, and Luke alone preserves the capstone about the mouth. Luke is telling the reader this is a teaching about words.

The Greek

Perisseuma (abundance): overflow, surplus, that which exceeds. The mouth speaks from what has overflowed the container. Not from calculation, not from performance, but from what is already full inside.

Thēsauros (treasure): a storehouse, a treasury, a place of deposit. The heart is a storeroom. Whatever has been deposited is what will be withdrawn.

Lalei (speaketh): present active indicative, continuous action. The mouth is habitually speaking out of the overflow. Not a one-off outburst, but the settled pattern of a person's speech.

Read together: the mouth is the point at which the storeroom of the heart overflows into audible reality, continuously. That is why speech is the fruit. Speech is the first place the heart shows itself, because speech is the nearest overflow.

Matthew 12:33-37 confirms it decisively

If Luke 6:45 left any ambiguity, Matthew 12:33-37 removes it. The Lord Jesus uses the same tree and fruit teaching and applies it explicitly and exclusively to words.

Either make the tree good, and his fruit good; or else make the tree corrupt, and his fruit corrupt: for the tree is known by his fruit. O generation of vipers, how can ye, being evil, speak good things? for out of the abundance of the heart the mouth speaketh. A good man out of the good treasure of the heart bringeth forth good things: and an evil man out of the evil treasure bringeth forth evil things. But I say unto you, That every idle word that men shall speak, they shall give account thereof in the day of judgment. For by thy words thou shalt be justified, and by thy words thou shalt be condemned.

Matthew 12:33-37 KJV

The arc is unmistakable: tree and fruit, then mouth speaking, then treasure of the heart, then idle words, then by thy words thou shalt be justified. The Lord Jesus does not let the metaphor drift into a general lesson about works. He lands it hard, twice, on speech. In Matthew 12 the fruit is the word, and the word is the ground of justification and condemnation. Two witnesses, Luke and Matthew, confirm the same interpretive centre.

The biblical theology of speech as primary fruit

Scripture consistently treats the tongue as the diagnostic organ of the inner man.

Proverbs 18:21, "Death and life are in the power of the tongue."
Proverbs 10:11, 20-21, 31-32, the mouth of the righteous as a well of life, choice silver, feeding many, bringing forth wisdom.
James 3:2, "If any man offend not in word, the same is a perfect man." James makes speech the diagnostic of maturity for the whole man.
Matthew 15:11, 18, "Not that which goeth into the mouth defileth a man; but that which cometh out of the mouth... those things which proceed out of the mouth come forth from the heart."
Romans 10:9-10, salvation itself structured around the mouth confessing what the heart believes.
2 Corinthians 4:13, "We having the same spirit of faith... we also believe, and therefore speak." Speech as the necessary overflow of believing.

Speech is not one fruit among many. In the biblical framework, speech is the revelatory fruit, the fruit that exposes the tree before any other fruit is examined. This is why the Lord Jesus makes it the interpretive key.

Why the common misapplication matters

When Luke 6:43-45 is used mostly for soul winning, partnership and works, three things go wrong.

First, the diagnostic gets externalised. The passage was designed to help a believer check the state of the heart by listening to habitual speech. Redirecting it to works allows a person to feel fruitful because of external activity while their speech quietly reveals a different treasure.

Second, the mouth line gets skipped. Most preaching reaches v.44 ("every tree is known by his own fruit"), defines fruit as works, and never engages the fact that the Lord Jesus Himself defined the fruit in v.45 as speech. The Master's own explanation is bypassed.

Third, the practical power of the teaching is lost. The reason the metaphor is grounded in the mouth is that speech is available for daily self-examination. Anyone can, at any moment, listen to what has been overflowing out of them in the last hour, the last day, the last week. Works are lagging indicators. Words are real-time indicators.

How speech and works fit together

There is no false dichotomy here. Scripture holds both together.

Speech is the primary fruit because it is the nearest overflow of the heart. It shows the treasure first. Works are the derived fruit because they follow the direction of the words. James 3 explicitly frames the tongue as a rudder that turns the whole body. Both are real fruit, but speech is causally prior. What a person consistently says directs and reveals what they will do.

The corrected order is: heart, then treasure, then overflow into speech, then direction of works. Luke 6:45 is diagnosing the source. Matthew 7 is examining the outcome. Neither cancels the other, but skipping the source diagnosis makes any examination of outcomes shallow.

The reading in one sentence

The Lord Jesus is not asking, "What are you doing?" He is asking, "What are you saying?" Because what a person is habitually saying is the overflow of what has been habitually stored, and what has been stored is the tree that will keep producing this same fruit until the treasure changes.

Related study threads

Trace the speech cluster in Luke 6:37-49 and note how many of the nine teachings concern words
Compare Colossians 3:16 with Ephesians 5:18, being filled with the word against being filled with the Spirit
Study thēsauros across the Gospels, including Matthew 6:21, where treasure and heart are tied together in the opposite direction
Trace James 3 as an extended commentary on Luke 6:45, particularly the rudder and the fountain