Rabanus Maurus
Catena Aurea · Matthäusevangelium 12
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.
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 shewn seem great, yet because of the carelessness of a cold heart, they receive a little reward from the Lord.