then it shall be, that whatever comes forth from the doors of my house to meet me, when I return in peace from the children of Ammon, it shall be Yahweh's, and I will offer it up for a burnt offering.
The writer wrote Judges 11:29-32 using a chiastic structure. This section begins and ends with the promise and fulfillment of God giving Jephthah victory. When the Spirit came on him there was no doubt that he would defeat the enemy. The center of the chiasm relates Jephthah bargaining with God to ensure victory. He did not need to make this vow. He had already testified that God had given His people victory in the past (Judges 11:21; Judges 11:24). Apparently his faith was not as strong as it might have been, and this weakness led him to seek a guarantee of success by making the vow.