John Gill Commentary Mark 7:19

"because it goeth not into his heart, but into his belly, and goeth out into the draught? [This he said], making all meats clean." — Mark 7:19 (ASV)

Because it enters 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 goes into the draught ;
(aokh tyb) , "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.