John 13:26

Jesus therefore answereth, He it is for whom I shall dip the sop, and give it to him. So when he had dipped the sop, he taketh and giveth it to Judas, the son of Simon Iscariot.

Westcott and others speak of the custom of giving a sop to an honored guest, inferring from this that Jesus here made one last effort to reach Judas' heart; but nothing like that is evident here. Jesus was identifying the traitor by an action often engaged in before, but not with the overtones of this situation. As soon as this was done, Judas knew that his identity was known to all but pretended that it was not true, saying, "Is it I?" Jesus told him plainly that it was indeed he (Matthew 26:25), and commanded him to "do quickly" what he had purposed to do (John 13:27).