John Chrysostom

(Hom. xlvii. 3) He tries to remove their difficulties in another way, as follows, It is the spirit that quickeneth, the flesh profiteth nothing: that is to say, You ought to understand My words in a spiritual sense: he who understands them carnally is profited nothing. To interpret carnally is to take a proposition in its bare literal meaning, and allow no other. But we should not judge of mysteries in this way; but examine them with the inward eye; i. e. understand them spiritually. It was carnal to doubt how our Lord could give His flesh to eat. What then? Is it not real flesh? Yea, verily. In saying then that the flesh profiteth nothing, He does not speak of His own flesh, but that of the carnal hearer of His word.