The saying about defilement from what comes into the mouth had scandalized the Pharisees; they had become so accustomed to the necessity of handwashing for spiritual cleanliness that they viewed Jesus' words as a challenge to their established rituals. They could also have been offended because Jesus directly addressed the crowd, undermining their authority.
In response to the news of the Pharisees’ offense, Christ either denounces their man-made doctrine, which does not derive from God and should thus be rejected, or He refers to the Pharisees themselves, suggesting they have deviated from God’s guidance. Though they are considered shepherds and instructors of the people, they are not God's chosen plants, meaning they do not follow God's laws and are not aligned with His will, thus lacking His favor. They are destined to fall away (cf. 13:29-30). Therefore, He urged to leave them be; this can be understood as both a warning to avoid their teachings or a call to cease worrying about them and let them be.
After this, Peter, speaking for all the disciples, requested clarification regarding the Lord’s perplexing statement about the nature of defilement linked to what enters or exits the mouth. The Lord clearly explained that what enters into the mouth refers to food, while what comes out signifies the evil thoughts, desires, and intentions that arise from the heart. The latter, as revealed through words, demonstrate the impurity of the human spirit, while food enters and exits the body without impacting the soul.