The Spirit came down upon Jephthah at this particular moment, for the purpose of the campaign, to embolden and strengthen him, empowering him to conquer the enemy. The Spirit was not upon him continuously, and not everything he said and did was inspired by the Spirit—for example, his negotiations with his tribesmen, his vow and its implementation, and his war with the Ephraimites.
29 Then the Spirit of the LORD was upon Jephthah, and he passed through Gilead and Manasseh and passed on to Mizpah of Gilead, and from Mizpah of Gilead he passed on to the Ammonites.