Charles Ellicott Commentary Matthew 12:33

"Either make the tree good, and its fruit good; or make the tree corrupt, and its fruit corrupt: for the tree is known by its fruit." — Matthew 12:33 (ASV)

Either make the tree good — Like most proverbs and parables, these words present different aspects and have various applications. As spoken to people of a neutral, half-hearted character, they might seem a call to consistency, not without a touch of indignant rebuke: “At least be thorough; let your principles and actions harmonize. Do not think you can produce the fruit of good works from the tree of a corrupt heart.”

This, however, is not their meaning here. The people to whom our Lord spoke were not neutral but in direct hostility to Him. Here, therefore, He presses on them the need for logical rather than practical consistency, telling them to “make”—that is, to reckon—the tree and its fruit as having the same character. If casting out demons is a good work, then the power from which it flows must also be good. Works of that kind do not come from a corrupt source.