Do not you yet understand, that whatever enters in at the mouth goes into the belly, and is cast out into the draught?…
Anselm says, "Our heart is like a mill, ever grinding, which a certain lord gave in charge to his servant, enjoining that he should only grind in it his master's grain, whether wheat, barley, or oats, and telling him that he must subsist on the produce. But that servant has an enemy, who is always playing tricks on the mill. If, any moment, he finds it unwatched, he throws in gravel to keep the stones from acting, or pitch to clog them, or dirt and chaff to mix with the meal. If the servant is careful in tending his mill, there flows forth a beautiful flour, which is at once a service to his master, and a subsistence to himself; but if he plays truant, and allows his enemy to tamper with his machinery, the bad outcome tells the tale; his lord is angry; and he himself is starved." This mill, ever grinding, is the heart; thoughts are the grain; the devil is the watchful enemy: he throws in bad thoughts, which can only be prevented by watchfulness and prayer.
Parallel VersesKJV: Do not ye yet understand, that whatsoever entereth in at the mouth goeth into the belly, and is cast out into the draught?