In the mystical sense, marriage signifies the union of Christ with his Church, because as the Apostle says: “This is a great mystery: I am speaking of Christ and his Church” (Eph 5:32).

And this marriage was begun In the womb of the Virgin, when God the Father united a human nature to his Son in a unity of person. So, the chamber of this union was the womb of the Virgin: “He established a chamber for the sun” (Ps 18:6).

Of this marriage it is said: “The kingdom of heaven is like a king who married his son” (Mt 22:2), that is, when God the Father joined a human nature to his Word in the womb of the Virgin.

It was made public when the Church was joined to him by faith: “I will bind you to myself in faith” (Hos 2:20). We read of this marriage: “Blessed are they who are called to the marriage supper of the Lamb” (Rv 19:9). It will be consummated when the bride, i.e., the Church, is led into the resting place of the groom, i.e., into the glory of heaven.

The fact that this marriage took place on the third day is not without it own mystery. For the first day is the time of the law of nature; the second day is the time of the written law. But the third day is the time of grace, when the incarnate Lord celebrated the marriage: “He will revive us after two days: on the third day he will raise us up” (Hos 6:3).

The place too is appropriate. For “Cana” means “zeal and “Galilee” means “passage.” So this marriage was celebrated in the zeal of a passage, to suggest that those persons are most worthy of union with Christ who, burning with the zeal of a conscientious devotion, pass over from the state of guilt to the grace of the Church: “Pass over to me, all who desire me” (Sir 24:26).

And they pass from death to life, i.e., from the state of mortality and misery to the state of immortality and glory: “I make all things new” (Rv 21:5).

Thomas Aquinas (1225-1274): Commentary on John, cap. 2, lect. 1, 338