An interesting enquiry on Twitter here:
Who is the very first commentator to apply to Rev 21:2 (the New Jerusalem) the analogy of Christ as bridegroom to his Church? I’m looking for the very beginnings of this tradition and a nice juicy source on its dissemination.
Let’s have Revelation 21:2 first:
21 Then I saw “a new heaven and a new earth,” for the first heaven and the first earth had passed away, and there was no longer any sea. 2 I saw the Holy City, the new Jerusalem, coming down out of heaven from God, prepared as a bride beautifully dressed for her husband. 3 And I heard a loud voice from the throne saying, “Look! God’s dwelling place is now among the people, and he will dwell with them. They will be his people, and God himself will be with them and be their God.
Probably the answer to this question is to consult some database of patristic references to scripture, like BIBLINDEX. Unfortunately this is very laborious to use.
Another alternative is to look at the Ancient Christian Commentary on Scripture (ACCS) series. There is a volume on Revelation, and this has quotations on Rev. 21:2.
The very interesting introduction (p.xx) informs us of commentaries in the west from the “commentary of Victorinus of Petovium through those of Tyconius, Primasius, Apringius, Caesarius of Arles, the Venerable Bede,” and later medieval writers. Victorinus died ca. 304. In the east “no Greek commentary of the Revelation appears before the sixth century (Oecumenius and Andrew of Caesarea), and that after the commentary of Arerhas (c. 900), who largely works over the commentary of Andrew of Caesarea, no additional commentary of significance arises…”.
On p.364 we find the material on Rev. 21:2. Three of these refer to the matter at hand.
It begins with Primasius:
By the testimony of the Truth this is the “city set on a hill.” Also Isaiah says, “The mountain of the house of the Lord shall be established as the highest of the mountains and shall be raised above the hills.”‘ [Isaiah says this] either because of the height of its righteousness, of which we read, ‘Your righteousness is like the mountains of God,” or because both the apostles and the prophets are called mountains. However, being more excellent than all others, the Lord Christ towers as a mountain above the heights of mountains, and from his fullness, it says, we receive grace for grace. Fittingly he says [that the city comes] down our of heaven from God, for [the church’s] beauty will then be seen more fully, when through the Spirit, by whom her bridegroom is believed to have been conceived and born, she has merited to bear the heavenly image. Therefore, it is this very bride that is this city. – Commentary on the Apocalypse 21.9-10.”
Next, Caesarius of Arles:
By the mountain he refers to Christ It is the church, the city established on the mountain, that is the bride of the Lamb. The city is then established on the mountain when on the shoulders of the Shepherd it is called back like a sheep to its own sheepfold. For were the church one and the city coming down from heaven another, there would be two brides, which is simply not possible. He has called this city the “bride” of the Lamb, and therefore it is clear that it is the church itself that is going to be described. – Exposition on the Apocalypse 21.10, Homily 19.
Finally Andrew of Caesarea:
That he was “carried away in the Spirit” indicates that through the Spirit he was elevated in his mind from earthly things to the contemplation of heavenly realities. The image of the “great mountain” indicates the sublime and transcendent life of the saints, in which the wife of the Lamb, the Jerusalem above, will be made beautiful and glorified by God. – Commentary on the Apocalypse 11.10-11.
The Venerable Bede is worth quoting also:
After the destruction of Babylon, the holy city, which is the bride of the Lamb, is seen located on a mountain. The stone which was cut out of the mountain without hands broke the image of the world’s glory into small pieces, and it grew into a great mountain and filled the whole world. Explanation oh the Apocalypse 21.10.
In truth the link between the New Jerusalem and the Church and Christ as the bridegroom is pretty obvious in the biblical text.
Now Primasius is supposed to be based on Tyconius and Augustine, De civitate Dei, 20.7-17. The latter is online in English here but I could not see any discussion of our point.
Tyconius has been reconstructed from Primasius recently, and an English translation of the reconstruction exists. Tyconius, Exposition of the Apocalypse, in: Fathers of the Church 134, (2017) p.181, is as follows:
 And I saw a new heaven and a new earth. For the first heaven and the first earth have gone away. And the sea is no more.  And I saw the holy city, new Jerusalem, coming down from heaven from God, prepared as a bride adorned for her husband.  And I heard a loud voice from heaven, saying: Behold, the tabernacle of God is with men; and he will dwell with them, and they will be his people, and God himself will be with them as their God.  And he will wipe away every tear from their eyes, and there will no longer be death, and there will no longer be pain. The first things have passed away.
He calls this “Jerusalem” the church, by recapitulating from the passion of Christ up to the day on which she rises and, having triumphed with Christ, she is crowned in glory. He mixes each time together, now the present, now the future, and declares more fully when she is taken with great glory by Christ and is separated from every incursion of evil people.
How this relates to the text of Primasius is not obvious, but not our concern here.
So our winner is … Tyconius!