Matthew 12:34
You brood of vipers, how can you who are evil say anything good? For out of the overflow of the heart the mouth speaks.
What it says
He calls them a brood of vipers and says evil hearts produce evil speech.
What it is doing
Their words reveal their condition.
In context
33Make a tree good and its fruit will be good, or make a tree bad and its fruit will be bad, for a tree is known by its fruit. 34You brood of vipers, how can you who are evil say anything good? For out of the overflow of the heart the mouth speaks. 35The good man brings good things out of his good store of treasure, and the evil man brings evil things out of his evil store of treasure. 36But I tell you that men will give an account on the day of judgment for every careless word they have spoken. 37For by your words you will be acquitted, and by your words you will be condemned.”