What does Matthew 15:13 mean?

The Pharisees believe themselves to be righteous keepers of God's laws. They also assume themselves the final authority on what it means to be a righteous keeper of these laws. Because of this, they expect God to bless them for their legalistic, careful adherence to these extended series of rules. From their perspective, anyone who disagrees with them also disagrees with God.

Jesus, however, has only had words of condemnation for these religious leaders. Previously, He called them hypocrites for elevating human tradition about handwashing to the level of doctrine. This, they did while diminishing God's actual commands, such as to honor parents (Matthew 15:1–9). The Pharisees have become so focused on legalistic rule-keeping that they have missed the intent of God's laws: the reason they exist in the first place. They have failed to take their opportunity to care for God's people and communicate to them the spirit of God's law.

This verse uses classic language from the Old Testament Scriptures to show that these Pharisees and scribes will be overthrown by God. Jesus calls them plants His Father has not planted; therefore, these religious leaders will not be protected by God from being uprooted and cast aside. This is harsh language on its own, but it would be devastating for those familiar with Israel's Scripture (Isaiah 60:21; 61:3; Jeremiah 17:8). This is even more devastating coming from the Son of God, Himself. God's blessings for Israel will not be given to the Pharisees of Jesus' day.