And Jephthah made a vow to the Lord: “If you give the Ammonites into my hands, whatever comes out of the door of my house to meet me when I return in triumph from the Ammonites will be the Lord’s.” Judges 11:30-31
There was no need for Jephthah to make this vow. The Spirit of the Lord had already come upon him (verse 29) and God was going to give him victory over the Ammonites. However, it seems Jephthah wasn’t willing to accept God’s freely given victory and tries to bargain for something God has already given him. In this way, Jephthah is trying to control God and make him operate according to his terms. Believing he can bargain his way to victory lessens his dependency on God.
How hard it is for human nature to embrace the free gift of God. We’re much more comfortable trying to earn them, bargain for them or in some way contribute to our salvation. We’d like to take some credit for our victories. Whether we try to impress God with our clever bargaining power or our showy devotion or our numerous good deeds, it’s all pointless. God will freely give but we must accept his gifts without trying to make ourselves worthy of them.
By making this vow Jephthah lost his daughter (and potential grandchildren), whether this was figuratively or literally is hard to say. Jewish thought would be that because he was prepared to sacrifice his daughter it doesn’t matter whether or not he did. It was possible under the law that Jephthah redeemed her and she served in the temple the rest of her life.
The point is though when we try to bargain with God or orchestrate circumstances to empower ourselves we dishonour God.