The Gospel is A Better and A Stronger Wine:

On the third day there was a wedding. What wedding can this be but the joyful marriage of man's salvation, a marriage celebrated by confessing the Trinity or by faith in the resurrection. That is why the marriage took place "on the third day," a reference to the sacred mysteries which this number symbolizes.

Hence, too, we read elsewhere in the Gospel that the return of the younger son, that is, the conversion of the pagans, is marked by song and music and wedding garments.

Like a bridegroom coming from his marriage chamber, our God descended to earth in his Incarnation, in order to be united to his Church which was to be formed of the pagan nations. To her he gave a pledge and a dowry: a pledge when God was united to man; a dowry when he was sacrificed for man's salvation. The pledge is our present redemption; the dowry, eternal life.

To those who see only with the outward eye, all these events at Cana are strange and wonderful; to those who understand, they are also signs. For, if we look closely, the very water tells us of our rebirth in baptism. One thing is turned into another from within, and in a hidden way a lesser creature is changed into a greater. All this points to the hidden reality of our second birth. There water was suddenly changed; later it will cause a change in man.

By Christ's action in Galilee, then, wine is made, that is, the law withdraws and grace takes its place; the shadows fade and truth becomes present; fleshly realities are coupled with spiritual, and the old covenant with its outward discipline is transformed into the new. For, as the Apostle says: The old order has passed away; now all is new! The water in the jars is not less than it was before, but now begins to be what it had not been; so too the law is not destroyed by Christ's coming, but is made better than it was.

When the wine fails, new wine is served: the wine of the old covenant was good, but the wine of the new is better. The old covenant, which Jews follow, is exhausted by its letter; the new covenant, which belongs to us, has the savor of life and is filled with grace.

Thy good wine, that is, good precepts, refers to the law; thus we read: You shall love your neighbor but hate your enemy. But the Gospel is a better and a stronger wine: My command to you is: love your enemies, pray for your persecutors.

  By Fautsus of Riez (5th c.),

The Lord was invited and came to a wedding. Is it any wonder that he who came to that house for a wedding came to this world for a wedding? ... Therefore he has a bride here whom he has redeemed by his blood and to whom he has given the Holy Spirit as a pledge. He wrested her from enslavement to evil, he died for her sins. He arose again for her justification. Who will offer such great things to his bride? Men may offer some trinket or other from the earth, such as gold, silver, precious stones, horses, slaves, farms or estates. Will any offer his blood? For if he gives his blood to his bride, he will not be alive to take her as his wife. But the Lord, dying free of anxiety, gave his blood for her in order that when he arose, he might have her whom he had already joined to himself in the womb of the Virgin. For the Word was the bridegroom, and human flesh was the bride.

from St. Augustine,