Judges 11:10

“And the elders of Gilead said unto Jephthah, etc.] Assenting to his proposal, and not only giving their word for it, but their oath: the Lord be witness between us, if we do not so according to thy words; that is, make him head over them; they appealed to the omniscient God, and called on him to be a witness of their agreement to it, and swore by him they would fulfil it; or if they did not, that the Lord would take vengeance on them for it, and punish the breach of this covenant and oath in some way or another; the Targum of Jonathan is, “the Word of the Lord be a witness between us, etc.””

“the elders of Israel said unto Jephthah, The Lord be witness between us--Their offer being accompanied by the most solemn oath, Jephthah intimated his acceptance of the mission, and his willingness to accompany them. But to make "assurance doubly sure," he took care that the pledge given by the deputies in Tob should be ratified in a general assembly of the people at Mizpeh; and the language of the historian, "Jephthah uttered all his words before the Lord," seems to imply that his inauguration with the character and extraordinary office of judge was solemnized by prayer for the divine blessing, or some religious ceremonial.”

“The Lord be witness - The Lord be an hearer: so the Hebrew word is. Whatever we speak it concerns us to remember, that God is an hearer! Judges 11:11”

“The Lord: Gen 21:23, Gen 31:50; Sa1 12:5; Jer 29:23, Jer 42:5; Rom 1:9; Co2 11:31 be witness: be the hearer, Gen 16:5, Gen 31:53; Deu 1:16; Sa1 24:12 if we do: Exo 20:7; Zac 5:4; Mal 3:5 Judges 11:11”

“The elders promised this on oath. "Jehovah be hearing between us," i.e., be hearer and judge of the things concerning which we are negotiating; "truly according to thy word so will we do" (לא אם, a particle used in connection with an oath). Judges 11:11”