Q. Why do a couple need a rabbi and ceremony in order to be married? Isn’t it enough to declare their vows to each other?
A. Maimonides says (Hil’chot Ishut 1:1) that before the Torah was given, a man and a woman saw each other, fancied one another, began to cohabit and that was that. Thereafter a ceremony in the presence of witnesses was required, and there are long halachic discussions about the details. The importance of the ceremony is because marriage is not only a private commitment between the parties but the creation of a home and, hopefully, a family, and the ceremony shows that the marriage, the home and the family are part of the community.