What is the earliest commentary on John 20:28?

Question

Thomas' statement at John 20:28

"Thomas replied, “My Lord and my God!”"

Ἀπεκρίθη Θωμᾶς καὶ εἶπεν αὐτῷ “Ὁ Κύριός μου καὶ ὁ Θεός μου.”

has been the subject of significantly different interpretations. Some, and now this seems the standard view, hold that Thomas is saying Jesus is both Thomas' Lord and God, where 'God' is understood in something like a Trinitarian sense.

There are other interpretations, including calling Jesus a 'god', an exclamation of astonishment, or Thomas seeing the Father in Jesus because he now knows Jesus is the agent of the Father.

What is the earliest known commentary on John 20:28? How does the commenter (or commenters if they are roughly contemporaneous) understand Thomas' statement?

Answer 1

Cyprian (210-258 AD) in his Three Books of Testimonies Against the Jews, in Book Two under item #6, "That Christ is God" references John 20:28 along with many other Scriptures as an accumulation of proofs that Christ is God. This writing predates Nicea by 100 years. The full relevant passage may be read here and a quote from the same is given below:

Also in the Gospel according to John: “In the beginning was the Word, and the Word was with God, and God was the Word. Also in the same: “The Lord said to Thomas, Reach hither thy finger, and behold my hands: and be not faithless, but believing. Thomas answered and said unto Him, My Lord and my God. Jesus saith unto him, Because thou hast seen me, thou hast believed: blessed are they who have not seen, and yet have believed...

Also Novatian (200-258 AD), again at least 100 years prior to Nicea, wrote the following in his Treatise Concerning the Trinity - chapter 13 (full text here) says:

Moreover, this Word “was in the beginning with God, and God was the Word.”5101 Who then can doubt, when in the last clause it is said, “The Word was made flesh, and dwelt among us,” that Christ, whose is the nativity, and because He was made flesh, is man; and because He is the Word of God, who can shrink from declaring without hesitation that He is God, especially when he considers the evangelical Scripture, that it has associated both of these substantial natures into one concord of the nativity of Christ? ... and if, finally, the Apostle Thomas, instructed in all the proofs and conditions of Christ’s divinity, says in reply to Christ, “My Lord and my God;” and if, besides, the Apostle Paul says, “Whose are the fathers, and of whom Christ came according to the flesh, who is over all, God blessed for evermore,” writing in his epistles; and if the same apostle declares that he was ordained “an apostle not by men, nor of man, but by Jesus Christ;” and if the same contends that he learned the Gospel not from men or by man, but received it from Jesus Christ, reasonably Christ is God.

And again, later in the same work, Novation says:

And let us therefore believe this, since it is most faithful that Jesus Christ the Son of God is our Lord and God; because “in the beginning was the Word, and the Word was with God, and God was the Word. The same was in the beginning with God. And, “The Word was made flesh, and dwelt in us. And, “My Lord and my God.. And, “Whose are the fathers, and of whom according to the flesh Christ came, who is over all, God blessed for evermore. What, then, shall we say? Does Scripture set before us two Gods? How, then, does it say that “God is one?” Or is not Christ God also? How, then, is it said to Christ, “My Lord and my God? ... let them understand that, from the fact that God is one, no obstruction arises to the truth that Christ also is declared to be God.”

Answer 2

This may not be the absolute earliest extant commentary, but if there were any earlier, I would think the popular Ancient Christian Commentary series would have included it. Unfortunately, the earliest post-dates the Council of Nicaea (AD 325).

From ACC Volume 21 (John 11-21) on John 20:28 My Lord and My God! (years approximate, my own addition):

The crucified Was God ATHANASIUS (AD 298-373): Let them therefore confess, even they who previously denied that the crucified was God, that they erred. For the divine Scriptures bid them, and especially Thomas, who, after seeing upon him the print of the nails, cried out, "My Lord and my God." -- Letter 59.10, To Epictetus (AD 372 or earlier)

Other quotes include:

• John Cassian (AD 360-435) from On the Incarnation of the LORD against Nestorius 6.19
• Augustine of Hippo (AD 354-430) from Sermon 14A
• Theodore of Mopsuestia (AD 350-428) from Commentary on John 7.20.27-29

For later Patristic commentaries, see this collection which includes complete commentaries by John Chrysostom (AD 347-407) and Cyril of Alexandria (AD 376-444).

Quote from extensive commentary by Cyril of Alexandria on John 20:28 showing a fully developed Trinitarian Christology:

... My Lord and my God. For we must all confess that it follows of a surety that He That is Lord by Nature and Ruler over all is also God, just as also universal dominion and the glory of sovereignty is clearly seen to appertain to the living God. Observe, too, that when he says My Lord and my God, he uses the article to show that there was One Lord and One God. For he does not say without the qualification of the article, My Lord and my God, to prevent any one from imagining that he called Him Lord or God as he might have done one of ourselves or of the holy angels. For there are gods many and lords many, in this sense, in heaven and on earth, as the wise Paul has taught us; but rather he recognises Him as, in a special sense, the One Lord and God, as begotten of the Father, Who is by Nature Lord and God, when he says, My Lord and my God; and, what is a still greater indication of the truth, the Saviour heard His disciple saying this, and saw that he rested in the firm conviction that He was, in fact, the Lord and God, and thought it not right to rebuke him. Christ, then, approved his faith, and with justice. And you may easily see that what I say is true. For to him that was possessed of this faith He says, at the end of the Gospel, as unto the rest: Go ye and make disciples of all the nations. And if He bids him who was thus minded teach all nations, and appointed him to instruct the world in His mysteries, He wishes us to have a like faith. For He is, in fact, Lord and God by Nature, even when Incarnate Man. For observe that the disciple, when he had touched His Hands, and Feet, and Side, made unto Him this confession of faith, not severing Emmanuel into a duality of Sons, but recognising Him as one and the same in the Flesh, for Jesus Christ is One Lord, according to the Scripture.