Some Christians have argued that the ancient Hebrews took marriage to be nothing more or less than a relationship instituted by consummation, i.e. by sexual relations. My understanding of Gordon Hugenberger's view in Marriage as a Covenant is that he takes the sexual act to be the initiation of the marriage, with the ceremony leading up to it counting as only a formality. The vows serve an important foundation of the comittment in marriage, but those vows are contingent on actually consummating the marriage. So a couple legally married who never consummate their marriage are not biblically married on his view. This is why Christians have often had no problem with divorce in such cases, and some even insist on calling it annulment, which means the marriage is treated as if it never really occurred. On Hugenberger's view, it never really did.
I've been inclined toward thinking that this was the view the ancient Hebrews assumed. After all, the marriage ceremony lasted something like a week, and during it the bride and groom are not married until the groom took the bride to his tent for their first sexual intercourse. However, if you assume this view and then read the Christmas narrative in Matthew, something doesn't seem right about Joseph's interaction with Mary. The text seems to indicate that he married her but didn't have sex with her until after Jesus was born. So what did their marriage consist of? What event initiated it? Not sex. On Hugenberger's view, sex is what makes it marriage. It's hard to see how that's consistent with this text.
Now this is surely an extraordinary event, since it involves a pregnancy that is itself an extraordinary event. Maybe that's enough to allow this to be an exception to what's generally true. But it still doesn't sit right with me, because it means marriage can't be defined the way Hugenberger defines it. In at least one instance a marriage is not initiated in the way his view requires. This is consistent with his view that any sexual interaction involves an implicit lifelong commitment. It's also consistent with the view that a marriage without consummation can be annulled. But it does seem to show that marriage can't be defined as a relationship initiated by sex.