Another insight from my husband:
God gave us free will. Why restrict it by taking oaths?
The reason that there is a ceremonial annulment of vows on the Judgement Day (Yom Kippur) once a year, is to restore our full free will.
A vow to God restricts our free will. If there is a vow we've forgotten about or uttered unintentionally, it still leaves a mark on our spiritual being. If we, even unknowingly, break it - it is a sin. If we keep it, it restricts our full range of potential actions as a human being.
How appropriate to do the vows annulment process during the time of judgement, the determination of our fortune for the next year. To fairly determine our portion for the future year, our being has to be capable of full range of potential action. Annulment of vows frees us to do just that.
