Jamieson, Fausset and Brown on Matthew 12:35

35. A good man, out of the good treasure of the heart, bringeth forth good things--or, "putteth forth good things":

and an evil man, out of the evil treasure, bringeth forth evil things--or "putteth forth evil things." The word "putteth" indicates the spontaneity of what comes from the heart; for it is out of the abundance of the heart that the mouth speaketh. We have here a new application of a former saying (see on Mt 7:16-20). Here, the sentiment is, "There are but two kingdoms, interests, parties--with the proper workings of each: If I promote the one, I cannot belong to the other; but they that set themselves in wilful opposition to the kingdom of light openly proclaim to what other kingdom they belong. As for you, in what ye have now uttered, ye have but revealed the venomous malignity of your hearts."