Charles Ellicott Commentary Matthew 26:21

"and as they were eating, he said, Verily I say unto you, that one of you shall betray me." — Matthew 26:21 (ASV)

One of you shall betray me — The words seem to have been intentionally vague, as if to rouse some of those who heard them to self-questioning. It is true, they had not shared in the Traitor's actual guilt, but they had yielded to tendencies they held in common with him, which were dragging them down to his level. They had joined him in his murmuring (Matthew 26:8); they had been quarreling, and were about to renew their quarrel, about precedence (Mark 9:34, Luke 22:24). It was good that the abyss was laid bare before their eyes, and that each should ask himself whether he was indeed on the point of falling into it.