Like a crown, God has adorned the earth with flowers, the heavens with stars, and the land with the sea. With a crown he has shown the special calling given to the holy kings, priests, prophets and apostles. In his bountiful mercy may he bless + these crowns through the prayers of the Mother of God and all the saints.
Then the groom is crowned with a wreath as the cantor sings from Psalm 21:2-5, and the priest continues:
May the Lord who crowned our holy fathers with justice look upon you with love. You have come to the holy Church seeking assistance, may the Lord bless you, protect you always, and lead you to everlasting life.
Then the bride is also crowned as the cantor sings from Psalm 45:11-14, and the priest continues:
May God who crowned all the holy women and blessed Sarah, Rebecca and Rachel, bless you, be merciful to you, and exalt you with the crown of glory. Adorned with fruits of the Spirit may you flourish as a blessed vine in the midst of the Church may the Lord God fill you with joy as you dwell with your husband in love and abiding peace; may you bring forth children pleasing to God; through the intercession of Mary, the Mother of God, and all the saints.
The specially designated witnesses are crowned as well.
The Melkites and Byzantine Catholics, about whom I know less, also do the same thing, with different ceremony, and I particularly like the Melkite hymn that is often sung: "O Lord our God, crown them with glory and honor, and grant them dominion over the works of your hands."
This sort of symbolism looks both ways, and are seen in quotations above. On the one hand, these are crowns of victory. As Chrysostom somewhat amusingly says in passing,
Youth is wild, and requires many governors, teachers, directors, attendants, and tutors; and after all these, it is a happiness if it be restrained. For as a horse not broken in, or a wild beast untamed, such is youth. But if from the beginning, from the earliest age, we fix it in good rules, much pains will not be required afterwards; for good habits formed will be to them as a law. Let us not suffer them to do anything which is agreeable but injurious; nor let us indulge them, as forsooth but children. Especially let us train them in chastity, for there is the very bane of youth. For this many struggles, much attention will be necessary. Let us take wives for them early, so that their brides may receive their bodies pure and unpolluted, so their loves will be more ardent. He that is chaste before marriage, much more will he be chaste after it; and he that practiced fornication before, will practice it after marriage. "All bread," it is said, "is sweet to the fornicator." Garlands are wont to be worn on the heads of bridegrooms, as a symbol of victory, betokening that they approach the marriage bed unconquered by pleasure. But if captivated by pleasure he has given himself up to harlots, why does he wear the garland, since he has been subdued?
Chrysostom's primary concern in context is completely elsewhere, but even in this passing reference we see the assumption of that the crown is "a symbol of victory". This past-looking element, that marriage is a state one wins through to is important, and I think increasingly overlooked in many discussions of 'singlehood' (which is not, as such, a state you win through to in any sense at all). And it is part of the dignity of marriage that you don't just fall into it: even to get there you have to win the privilege of the other person's consent. In turn, the point reflects on the dignity of human nature itself: the privilege of your consent is something worthy of being won.
The crowns are not merely victor's crowns, though; they look forward as well. We see this in the Melkite hymn quoted above: "crown them with glory and honor, and grant them dominion". I find the subtle insight of the second point particularly interesting. It's a reference to the story in Genesis 1, of course, and makes the point, often forgotten, that when God commands humanity to rule over fish and bird and living creature, it is to humanity as "male and female" who are to "be fruitful and multiply". All marriages are royal marriages.
I took a class once in college, years ago, on Wisdom Literature in the Old Testament, and one of the books required for the class used one of these deconstruction-reconstruction approaches to the text, or, rather, what some theologians today call 'deconstruction' and reconstruction, since it has only the loosest connection with serious deconstruction. In any case, it involves "exploring the problematics of the text", i.e., going out of your way to find something, anything, that could be regarded as a sign of bias in the text, regardless of how strained it may be. And in the discussion of the Song of Songs, the author pinned down one of the biases of the text as "crypto-monarchist" in its evaluational vocabulary. I've always thought that was rather laughably absurd; there is no "crypto" about it. You have only to read the book to see that it is explicitly using language for royalty and royal courts to evaluate the love between the Shulamite and her lover positively. And this is even more clear when you think through many of the metaphors by which the lover and the beloved describe each other: they are metaphors of military power, great wealth, vast territory, and courtly accompaniment. And how could it be otherwise? The whole point of a love song like this is that the crown of love is a more splendid wealth and dominion than any material kingdom. And this is a sense of things found throughout the world, among men and women alike: There is a royal dignity in such things.
If this is true in some degree of every marriage, then it is especially true of that marriage that serves as sign and symbol of the union of Christ and His Church, which is what the sacrament of Matrimony or mystery of Crowning designates. Christian marriage is always a sign of the Kingdom of God; even the botched ones that are at best defective signs of it. Marriage is a coronation.