John Chrysostom — as excerpted in the Catena Aurea on John 18:15-18

“He omits his own name out of humility: though he is relating an act of great virtue, how that he followed when the rest fled. He puts Peter before himself, and then mentions himself, in order to shew that he was inside the hall, and therefore related what took place there with more certainty than the other Evangelists could. That disciple was known unto the high priest, and went in with Jesus into the palace of the high priest. This he mentions not as a boast, but in order to diminish his own merit, in having been the only one who entered with Jesus. It is accounting for the act in another way, than merely by greatness of mind. Peter’s love took him as far as the palace, but his fear prevented him entering in: But Peter stood at the door without.”