John Chrysostom — as excerpted in the Catena Aurea on Matthew 16:13-19

“And truly if Peter had not confessed that Christ was in a peculiar sense born of the Father, there had been no need of revelation; nor would he have been worthy of this blessing for confessing Christ to be one of many adopted sons; for before this they who were with Him in the ship had said, Truly thou art the Son of God. (John 1:49.) Nathanael also said, Rabbi, thou art the Son of God. Yet were not these blessed because they did not confess such sonship as does Peter here, but thought Him one among many, not in the true sense a son; or, if chief above all, yet not the substance of the Father. But see how the Father reveals the Son, and the Son the Father; from none other comes it to confess the Son than of the Father, and from none other to confess the Father than of the Son; so that from this place even it is manifest that the Son is of the same substance, and to be worshipped together with the Father. Christ then proceeds to shew that many would hereafter believe what Peter had now confessed, whence He adds, And I say unto thee, that thou art Peter,”