John Gills Exposition of the Bible Commentary

Verse 19 (Mark 7:19)

Because it entereth not into his heart ,.... Which is the seat and fountain of all moral pollution; and if that is not defiled, no other part can be; and that that is not defiled by eating and drinking, unless in case of intemperance, is clear; because food and drink do not go into it:

but into the belly ; it is taken in at the mouth, goes down the throat, and is received into the stomach, and from thence it passes through the bowels:

and goeth into the draught ; בית הכסא , "the private house", as the Jews call it, without going into the heart at all:

purging all meats ; that which it leaves behind, is pure and nourishing; and whatever is gross and impure, is carried with it into the draught, so that nothing remains in the man that is defiling.

- John Gills Exposition of the Bible Commentary