Charles Ellicott Commentary John 21:7

"That disciple therefore whom Jesus loved saith unto Peter, It is the Lord. So when Simon Peter heard that it was the Lord, he girt his coat about him (for he was naked), and cast himself into the sea." — John 21:7 (ASV)

Therefore that disciple whom Jesus loved saith unto Peter,—Compare Introduction, p. 375. The traits of character that we have encountered before are exactly preserved here. John, true to the life of contemplation, is first to trace in the present catch of fish an analogy with the earlier one, and to discern that the Master who spoke then is present now. Peter, true to the life of action, is first to rush into that Master’s presence when he is told that it is the Lord.

He girt his fisher’s coat unto him (for he was naked),—That is, as the words in the original clearly imply, he put on, and girded around his body the garment that workmen customarily used. This seems to have been a kind of linen frock worn over the shirt, and the Talmud has adopted the Greek word used here to express it. The word occurs nowhere else in the New Testament, and the rendering “fisher’s coat” probably gives a correct idea of what is meant.

The common usage of the Greek and Hebrew words corresponding to the English word “naked,” makes it probable that Saint Peter was wearing some undergarment, and that reverence for the Lord, into whose presence he was about to go, led him to add to this the outer frock. .