Jewish marriage is a two-step process: The first stage is called kiddushin; the second, nisuin. The first is classically performed through the groom giving his bride a ring and stating, "Harei at mikudeshes li" ("You are hereby betrothed to me"), and the second, through the chuppah (canopy) ceremony.
Kiddushin is closely associated with hekdesh, the term that refers to sanctified objects. Through kiddushin a man prohibits his wife just as hekdesh items are prohibited from all benefit.
In other words, the groom "sanctifies" his bride.
Intriguing.
But here is where it gets truly interesting.
After kiddushin the bride is prohibited to all people, but she is not yet fully married to her husband. In fact, she is (rabbinically) prohibited even to him! She becomes permissible to him only after the second step, nisuin.
Isn't this odd? What is the point of dividing the marriage into two steps and to prohibit her even to her own husband? Where's the benefit?
Even more strange is the berachah we recite when a couple marries.
... that You have sanctified us with Your mitzvos and commanded us about the arayos, and prohibited to us the arusos (the betrothed women, after the kiddushin but before the nisuin), and permitted to us those married to us through chuppah and kiddushin. Blessed are You, Hashem, Who sanctifies His nation through chuppah and kiddushin.
What a strange blessing!
Since when do we make a blessing on a prohibition (You prohibited to us the arusos)? Why not simply say a blessing on the mitzvah of kiddushin?
And the conclusion is also strange: What do we mean by saying that Hashem sanctifies us through chuppah and kiddushin? He sanctifies us through all the mitzvos, as we said at the beginning of this very berachah (that You have sanctified us with Your mitzvos)!
It would seem that the entire formula of this blessing is an extended praise to Hashem for establishing the kiddushin/nisuin system ... which brings us back to our initial point. What is the significance of this system?
Let's reiterate the point with one additional source. The Rambam writes: "Before the Torah was given, if a man met a woman in the market and they both consented, he brought her home and lived with her ... After the Torah was given he must acquire her (through kiddushin) first" (Rambam, Hil. Ishus 1:1).
What is kiddushin?
It is kedushah ... separation.
It conveys that a Jew does not marry on instinct and impulse, after meeting a woman in the street. It suggests that a Jew's marriage is not analogous to the natural order followed by everything else on earth. A Jew's marriage is not just another example of mindless cause and effect, of the universal instinct to procreate.
Kiddushin is a separation from what comes naturally; it is a pause button.
A woman is indeed your wife after kiddushin, but a wife who is prohibited to you. You must relate to her in a different way. She is a vehicle through which you will be marbeh kevod Shamayim. She is kadosh, sanctified.
Indeed, all the mitzvos convey that Klal Yisrael rises above the natural order, but perhaps none more than the process of kiddushin and chuppah, which suggests that even marriage, that which seems so instinctual ... is in fact so much more. And so we thank Hashem, Who "sanctifies us through chuppah and kiddushin."