Jesus tells the Pharisees that they need to look and see if they are as clean on the inside as they appear to be on the outside. Jesus came to save these people from sin, but this requires that he save them from BOTH the guilt AND the practice of sin. But instead of thanking him for his help they get angry and resist him.
As we take the Lord‘s Supper, we need to remember that Jesus came to save US from both the guilt and the practice of sin. Sometimes Jesus has to tell us to look inside and see if we are as clean on the outside as we appear to be on the inside. Sometimes he has to tell us through the scriptures or through his people to stop neglecting the important things. And when Jesus tells us we are doing something wrong, we must learn to submit and respond in a gracious way. This is the only way by which he can change our behavior and so save us from both the guilt AND the practice of sin.