Albert Barnes Commentary John 13:26

"Jesus therefore answereth, He it is, for whom I shall dip the sop, and give it him. So when he had dipped the sop, he taketh and giveth it to Judas, [the son] of Simon Iscariot." — John 13:26 (ASV)

Jesus answered. That is, he answered John. It does not appear that either Judas or the other apostles heard him.

Shall give a sop. The word translated sop means a morsel, a piece of bread, or anything else eaten—as much as we are accustomed to take at a mouthful. Jesus was about to dip it in the sauce which was used at the Passover.

The word dip, in the original, is that from which is derived the word baptize. It means here that Jesus would dip it into the sauce as we do a piece of bread.

It is probable that it was not an unusual thing for the master of a feast to help others in this way, as it does not appear to have attracted the attention of the others as at all remarkable. It was an indication to John who the betrayer was, and a hint which Judas also probably understood.