In the Commentary on John, St. Thomas Aquinas writes the following about marriage:
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.