The first thing to be careful about is that you do not make a vow that is contrary to God's will—or that can bring you into conflict with it. An example of a vow that brought someone into conflict with God’s commandment is the vow that Jephthah made. Jephthah does this before the battle with the Ammonites. Then he makes this vow: If you will give the Ammonites into my hand, then whatever comes out from the doors of my house to meet me when I return in peace from the Ammonites shall be the Lord’s and I will offer it up for a burnt offering
(Judges 11:30–31).
Jephthah did not think carefully when making this vow. The Lord does give him victory, and when he comes home, the first to meet him from his house is his daughter! What grief! Jephthah has put himself in a difficult position through careless words. This situation implies that Jephthah is not allowed to carry out his vow. Yet he has brought guilt upon himself and he should confess it to God. The sad reality is that Jephthah did carry out his vow (Judges 11:39).
When you make a vow and do not think it through carefully, carrying out that vow may cause you serious harm. If that is true, yet it does not put you into conflict with God's law, you should still keep your vow. Then every apology is a waste. Then you should not use words like, I made a mistake; I did not mean it that way.
The Spirit says in Psalm 15:4 [NASB], A despicable person is despised in his eyes, but he honours those who fear the Lord; He takes an oath to his own detriment, and does not change.
5 It is better that you should not vow than that you should vow and not pay.