“But the things that come out of the mouth come from the heart, and these things defile a person.”
Jesus taught on true defilement. Ceremonial uncleanness pointed toward the greater evil. The inner person is the source of unholiness and profane one’s words and actions.
Conversion from the heart and control of the mind are necessary to one’s sanctification. From evil thoughts that enter will come evil words and sins. It cannot be otherwise.