What does Matthew 12:33 mean?

The Pharisees are enduring another rebuke from Christ. This comes in the aftermath of their unforgivable sin: to associate a miracle from Christ with Satanic power (Matthew 12:22–32). These kinds of interactions would have surprised many people of first-century Israel: the Pharisees were thought to be the best example of good. They posed as the model of faithfulness to God. As strict legalists, they measured their righteousness by keeping lists of rules and regulations, which were far more restrictive than the actual laws given through Moses.

Rather than praising their behavior, Jesus bluntly condemns them. It's common sense to judge the quality of a fruit tree by looking at what it produces: good or bad fruit. The Pharisees have shown their spiritual "fruit" in accusing Jesus of blasphemy for claiming to be the Messiah. They have revealed the real nature of their hearts by claiming His power to cast out demons comes from Satan. In truth, they are the ones guilty of blasphemy.

In the final judgment, faith in Christ is the line in the sand (John 14:6). It's either the One, or nothing at all (John 3:36). Anyone who does not recognize Him as the Messiah is on the bad side of that line. By making such an obvious, hard-hearted attempt to reject Him (Matthew 12:24), the Pharisees leave no room to claim they merely made a mistake or didn't get it. Their rejection of Him shows they are actually evil in their hearts.