Albert Barnes on Matthew 12:33

Either make, etc. The fact asserted in this verse is, that a tree is known not by its leaves, or bark, or form, but by its fruit. The application to the argument is this: "You are to judge of man's being in league with Satan by his works. If my doctrines and works be properly the works of Satan, then I am corrupt; if not, then your charge is blasphemy. So, on the other hand, if, not withstanding your professions, your works are the works of the devil, and your doctrines be such as he would teach, it would prove respecting you that which you charge on me." In this indirect but powerful manner, he advances to the charge against them, which he urges in the following verses.