Completely a side point, but it's something that I ran across a few years ago when I started this pledge research and have never remarked upon before.
Many academics believe that early Christianity was a product of rabbinic Judaism. Since rabbinic Judaism strongly opposes vows and pledges, when I started the virginity pledge research I briefly looked at the Christian texts to see what they had to say about vows.
The view at least in the Sermon on the Mount seemed similar to the rabbinic view, that vows were forbidden.
Somehow, though, the US acquired many pledges and vows, such as swearing in for political office, testimony in court, the original alcohol abstinence pledges in the 19th century which also came out of religious movements, and now the virginity pledge.