I was just sharing this with someone on another forum yesterday, so I will just copy and paste the whole thing:
For there is no good tree which produces bad fruit, nor, on the other hand, a bad tree which produces good fruit. For each tree is known by its own fruit. For men do not gather figs from thorns, nor do they pick grapes from a briar bush. The good man out of the good treasure of his heart brings forth what is good; and the evil man out of the evil treasure brings forth what is evil; for his mouth speaks from that which fills his heart. (Luke 6:43-45)
If you read in Matthew, Jesus made another statement about treasure, saying:
Therefore every scribe who is instructed unto the Kingdom of Heaven is like unto a man that is a householder, who brings forth out of his treasure things new and old. (Matthew 13:52).
What He meant here was that those who will receive revelation from the Spirit of God will bring forth meaning from both the Old Testament and also shed light on what in means in the New Testament era by expounding on what God had actually been saying all along, on things like how the gospel was always intended to be extended to the Gentiles, only it was "a mystery hidden in God."
So this "treasure" here referred to revelation from God concerning His word. So too in the first passage. "The good man out of the good treasure of his heart brings forth what is good, and the evil man out of the evil treasure brings forth what is evil" means that a good man will bring forth good "treasure," i.e. accurate revelation from God, and an evil man will utter false teachings. Both of them will "treasure" the things they believe, but one will teach truth and the other falsehoods.
That the "figs and grapes" are actually teachings is also suggested by the fact that Jesus talked about men "gathering" them, and this is what people do when they find a good teacher. They will sit under them and "gather" in the things they are teaching as being something they wish to "eat" spiritually, as good spiritual food.
If you look at the parallel passage in Matthew, the same thing becomes apparent, because Jesus there combined the teaching with discussing what false prophets would teach:
15 Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves. 16 Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles? 17 Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit. 18 A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. 19 Every tree that bringeth not forth good fruit is hewn down, and cast into the fire. 20 Wherefore by their fruits ye shall know them. 21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that does the will of my Father which is in heaven. 22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works? 23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity. (Matthew 7:15-23).
False prophets prophesy, and the things they prophesy are the main things people "gather in" from them. But the fruit they are speaking is bad fruit, and will not bring eternal life and health but spiritual corruption. This is also evident in what He said about the false prophets in Matthew 24. He told the disciples:
24 For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect. 25 Behold, I have told you before. 26 Wherefore if they shall say unto you, Behold, he is in the desert; go not forth: behold, he is in the secret chambers, believe it not. 27 For as the lightning cometh out of the east, and shines even unto the west; so shall also the coming of the Son of man be. 28 For wheresoever the carcass is, there will the vultures be gathered together. (Matthew 24:24-28).
He was saying that unlike Him, these false prophets and false Christs will be like "carcasses" or spiritually dead men, and the vultures will be their followers, who will gather around them to eat of their dead and corrupted teachings.
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That may be more teaching than what you wee asking for, but it all kinda goes together, so I just pasted the whole thing for you.
There's also the passage about "If you have not been faithful in unrighteous mammon, who will commit unto your trust the true riches," and this was also talking about the same thing. The riches here are the treasures of true revelation from God, i.e. accurate teachings, that we must be faithful to minister unto others.