Judges 11:30
And Jephthah vowed a vow unto the LORD, and said, If thou shalt without fail deliver the children of Ammon into mine hands, And Jephthah vowed a vow unto the LORD, and said, If thou shalt without fail deliver the children of Ammon into mine hands,
The vow stands within the history of Jephthah, whom God raised up as a deliverer for Israel against the Ammonites. It was uttered as he went out to confront that enemy in battle. It followed eighteen years in which Israel had suffered under Ammonite oppression. That long affliction came to an end when Jephthah fought the Ammonites and broke their power. The wider setting of the vow is a further turning away, for Israel soon forgot the lesson that its suffering had been meant to teach.