Augustine of Hippo — as excerpted in the Catena Aurea on John 13:12-20

“(Tr. xlix. 2) The Arians, when they hear this passage, appeal immediately to the gradations in their system, that as far as the Apostle is from the Lord, so far is the Son from the Father. But our Lord hath left us no room for doubt on this head; for He saith, I and My Father are one. (supr. 10:30) But how shall we understand those words of our Lord, He that receiveth Me, receiveth Him that sent Me? If we take them to mean that the Father and the Son are of one nature, it will seem to follow, when He says, He that receiveth whomsoever I send, receiveth Me, that the Son and an Apostle are of one nature. May not the meaning be, He that receiveth whosoever I send, receiveth Me, i. e. Me as man: But He that receiveth Me, i. e. as God, receiveth Him that sent Me. But it is not this unity of nature, which is here put forth, but the authority of the Sender, as represented by Him who is sent. In Peter hear Christ, the Master of the disciple, in the Son the Father, the Begotten of the Only Begotten.”