The once and for all sacrifice for sins is Jesus Christ once in for all for mankind. All the sacrifices in these books show forth of the ultimate sacrifice of Jesus Christ. It is better not to vow at all then to break it, God is not requiring anyone to make a vow. A vow is done on our part towards God and He will honor it if its done right. If you make a vow unto the Lord it is very important to keep it. We have in the Old Testament that were unfortunate and were bad vows. A married women that makes a vow the husband can disallow the vow, if not it because a binding vow. In the 30th chapter of numbers it s the laws of vows.
