Numbers - Chapter 30

This chapter is all about vows:

When a man makes a vow to the Lord or takes an oath to bind himself by a pledge, he must not break his word but must do everything he said,

The best commentary on this chapter is provided by Jesus himself, during the sermon on the Mount, recorded in Matthew chapter 5:

"You have also heard that our ancestors were told, ‘You must not break your vows; you must carry out the vows you make to the Lord.’ But I say, do not make any vows! Do not say, ‘By heaven!’ because heaven is God’s throne. And do not say, ‘By the earth!’ because the earth is his footstool. And do not say, ‘By Jerusalem!’ for Jerusalem is the city of the great King. Do not even say, ‘By my head!’ for you can’t turn one hair white or black. Just say a simple, ‘Yes, I will,’ or ‘No, I won’t.’ Anything beyond this is from the evil one."