John 21:20

In these verses, we have, I. The conference Christ had with Peter concerning John, the beloved disciple, in which we have, 1. The eye Peter cast upon him (Joh 21:20): Peter, in obedience to his Master's orders, followed him, and turning about, pleased with the honours his Master now did him, he sees the disciple whom Jesus loved following likewise. Observe here, (1.) How John is described. He does not name himself, as thinking his own name not worthy to be preserved in these records; but gives such a description of himself as sufficiently informs us whom he meant, and withal gives us a reason why he followed Christ so closely. He was the disciple whom Jesus loved, for whom he had a particular kindness above the rest; and therefore you cannot blame him for coveting to be as much as possible within hearing of Christ's gracious words during those few precious minutes with which Christ favoured his disciples. It is probable that mention in here made of John's having leaned on Jesus's breast and his enquiring concerning the traitor, which he did at the instigation of Peter (Joh 13:24), as a reason why Peter made the following enquiry concerning him, to repay him for the former kindness. Then John was in the favourite's place, lying in Christ's bosom, and he improved the opportunity to oblige Peter.

— Matthew Henry's Concise Commentary (public domain)

Peter, turning about--showing that he followed immediately as directed. seeth the disciple whom Jesus loved following; which also leaned on Jesus' breast at supper, and said, Lord, which is he that betrayeth thee?--The Evangelist makes these allusions to the peculiar familiarity to which he had been admitted on the most memorable of all occasions, perhaps lovingly to account for Peter's somewhat forward question about him to Jesus; which is the rather probable, as it was at Peter's suggestion that he put the question about the traitor which he here recalls (Joh 13:24-25).

— Jamieson-Fausset-Brown Commentary (public domain)