What does Matthew 15:8 mean?

Jesus has called these Pharisees hypocrites right to their faces. After pointing out that they are using tradition to give people an exemption from God's command to honor their parents, Jesus has declared that they are making the Word of God nothing (Matthew 15:4–6).

Now Jesus is applying a prophecy from Isaiah 29:13 to the Pharisees. These are words the Lord gave to Isaiah to say to the people. Jesus makes clear that these words apply to the men standing in front of Him, as well.

The Lord said to Isaiah that the Israelites were honoring Him only with their words, but not with sincerity or truth. They were going through the motions of religion. They put on a show by saying all the right things at the right times. They were not committed to God in their hearts, however. They were devoted to a religious system, not to the God it was meant to honor.