Chrysostom: "But as speaking not for Himself but for the Holy Spirit, He accordingly rebukes them, saying, Generation of vipers, how can ye being evil speak good things? This is both a rebuke of them, and a proof in their own characters of those things which had been said. As though He had said, So ye being corrupt trees cannot bring forth good fruit. I do not wonder then that you thus speak, for you are ill nourished of ill parentage, and have an evil mind. And observe He said not, How can ye speak good things, seeing ye are a generation of vipers? for these two are not connected together; but He said, How can ye being evil speak good things? He calls them generation of vipers, because they made boast of their forefathers; in order therefore to cut off this their pride, He shuts them out of the race of Abraham, assigning them a parentage corresponding to their characters."
Rabanus Maurus: "Or the words, Generation of vipers, may be taken as signifying children, or imitators of the Devil, because they had wilfully spoken against good works, which is of the Devil, and thence follows, Out of the abundance of the heart the mouth speaketh. That man speaks out of the abundance of the heart who is not ignorant with what intention his words are uttered; and to declare his meaning more openly He adds, A good man out of the good treasure of his heart bringeth forth good things. The treasure of the heart is the intention of the thoughts, by which the Judge judges that work which is produced, so that sometimes though the outward work that is shown seem great, yet because of the carelessness of a cold heart, they receive a little reward from the Lord."
Chrysostom: "Herein also He shows His Godhead as knowing the hidden things of the heart; for not for words only, yea but for evil thoughts also they shall receive punishment. For it is the order of nature that the store of the wickedness which abounds within should be poured forth in words through the mouth. Thus when you shall hear any speaking evil, you must infer that his wickedness is more than what his words express; for what is uttered without is but the overflowing of that within; which was a sharp rebuke to them. For if that which was spoken by them were so evil, consider how evil must be the root from whence it sprung. And this happens naturally; for oftentimes the hesitating tongue does not suddenly pour forth all its evil, while the heart, to which none other is privy, begets whatsoever evil it will, without fear; for it has little fear of God. But when the multitude of the evils which are within is increased, the things which had been hidden then burst forth through the mouth. This is that He says, Out of the abundance of the heart the mouth speaketh."
