What does Matthew 15:7 mean?

The Pharisees who traveled from Jerusalem to Galilee to confront Jesus may have been wishing they stayed home after this exchange. Not only did their accusation about ritual handwashing not land with Jesus, He turned it into an opportunity to call out their own practice of putting tradition above an actual command of God.

Traditional interpretation of God's commands about charity became a loophole: allowing people to declare some of their money and goods as being devoted to God, while keeping those things and using them. It may even have been possible to annul their vow later if they chose to. The problem was that if something was devoted to God in this way, people were free not to use it to care for their aging parents. It was a dodge, giving the people a way to avoid providing for their father and mother in their later years.

Jesus called out this attempt to avoid the spirit of the fifth commandment. For the sake of this tradition, the Pharisees are making void the Word of God. He calls these respected men hypocrites, right to their faces. He applies to them Isaiah's condemnation from the Lord of the Israelites of his day. That passage from Isaiah 29:13 fits these Pharisees perfectly. It was likely a passage they knew well.