A.T. Robertson Commentary Matthew 15:17

"Perceive ye not, that whatsoever goeth into the mouth passeth into the belly, and is cast out into the draught?" — Matthew 15:17 (ASV)

Perceive ye not? (ου νοειτε). Christ expects us to make use of our νους, intellect, not for pride, but for insight. The mind does not work infallibly, but we should use it for its God-given purpose. Intellectual laziness or flabbiness is no credit to a devout soul.