Jesus labeled these Jews hypocrites because they were not sincere in their actions. They knew what the law required of them but avoided doing it under the pretense of obeying the traditions of the elders. They claimed to be true worshippers of God but were not.
Jesus applied the prophecy of Isaiah 29:13 to these people to rebuke them for their impure hearts. Yes, their words honored God, but their motives were impure. For example, they pretended to be righteous as they piously claimed that their money had been pledged to God as a gift and couldn't be used to help their parents, but their hearts were full of evil intentions. God demands clean lips and clean hearts from those who would worship Him! If our hearts are not right before God, our words--no matter how seemingly noble--will be useless.
"In vain they worship Me, teaching as doctrine the commandments of men" (Matt. 15:9). Man's worship of God is useless as long as he teaches human traditions as divine doctrine (cf. John 4:24). We must be good students of God's word so we will always be able to identify the difference between divine doctrine and traditions originating with men. If we are ignorant of the difference between these two categories, our worship will also be vain before God.
Not only did the scribes and Pharisees elevate their traditions to the status of divine doctrine, but in some cases they tragically rejected God's commands in order to keep their own traditions (cf. Mark 7:9)!
Jesus then proceeded to exhort the multitude to listen closely and comprehend what He is about to say. He is going to instruct them as to where real defilement comes from.
Matthew 15:11 - "Not what goes into the mouth defiles a man; but what comes out of the mouth, this defiles a man." Food, drink, or dirty hands do not defile one's character; sinful thoughts, words, and deeds defile one's character. Jesus is not saying that these Jews should disregard the Mosaic laws that restricted their diet (cf. Lev. 11). Jesus is saying that "to eat with unwashed hands does not defile a man" (Matt. 15:20). The converse is also true: Purity of character is not created or guaranteed because one eats with clean hands (had the scribes and Pharisees ever considered this?). Jesus is laying down the principle that nothing physically ingested can defile the character of an individual, but disobedience to God does defile.
In the Christian age, there are no dietary restrictions similar to those found in the Old Testament other than the prohibition of eating blood (cf. Acts 15:29). If one were to drink blood today, he would be defiled, but not because the consumption of blood makes one's soul impure. Rather, he would be defiled because he has disobeyed God.
There is nothing wrong with washing one's hands before eating. In fact, it's a good idea for several reasons. However, one who eats with dirty hands isn't defiled before God as a result. To teach otherwise is to bind a tradition of men.
We will conclude our study of this context in our next lesson.