Who Says It

Rambam’s certainty this is a birchat ha-mitzvah shows itself also in his view that the groom—the one performing the mitzvah—should recite the blessing (or his messenger). Beit Shemu’el disagreed for a technical reason, we generally do not require people to perform rare ceremonies, to not embarrass the ignorant. Just as we have someone read the Torah on behalf of the person called up for the aliyah and for farmers who bring first fruits—each theoretically supposed to read himself—we have someone else read it here.

AH offers a more conceptual idea, we in fact see it as a blessing on the sanctity of the Jewish people, making others equally appropriate to recite the blessing.