John Calvin Commentary 1 Corinthians 11:29

"For he that eateth and drinketh, eateth and drinketh judgment unto himself, if he discern not the body." — 1 Corinthians 11:29 (ASV)

He who shall eat unworthily, eats judgment to himself. He had previously pointed out in express terms the heinousness of the crime, when he said that those who eat unworthily would be guilty of the body and blood of the Lord. Now he alarms them by denouncing punishment, for there are many who are not affected by the sin itself, unless they are struck down by the judgment of God. This, then, is what he does when he declares that this food, otherwise health-giving, will turn out to their destruction and will be converted into poison for those who eat unworthily.

He adds the reasons: because they do not distinguish the Lord’s body, that is, as a sacred thing from the profane. “They handle the sacred body of Christ with unwashed hands (Mark 7:2), even more, as if it were a thing of no importance, they do not consider how great its value is. They will therefore pay the penalty for such a dreadful profanation.” Let my readers keep in mind what I stated previously: that the body is presented to them, though their unworthiness deprives them of participation in it.