A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
jdg 11:1JEPHTHAH. (Jdg 11:1-3)
son of an harlot--a concubine, or foreigner; implying an inferior sort of marriage prevalent in Eastern countries. Whatever dishonor might attach to his birth, his own high and energetic character rendered him early a person of note.
Gilead begat Jephthah--His father seems to have belonged to the tribe of Manasseh (Ch1 7:14, Ch1 7:17).
jdg 11:2Thou shalt not inherit in our father's house--As there were children by the legitimate wife, the son of the secondary one was not entitled to any share of the patrimony, and the prior claim of the others was indisputable. Hence, as the brothers of Jephthah seem to have resorted to rude and violent treatment, they must have been influenced by some secret ill-will.
jdg 11:3Jephthah . . . dwelt in the land of Tob--on the north of Gilead, beyond the frontier of the Hebrew territories (Sa2 10:6, Sa2 10:8).
there were gathered vain men to Jephthah--idle, daring, or desperate.
and went out with him--followed him as a military chief. They led a freebooting life, sustaining themselves by frequent incursions on the Ammonites and other neighboring people, in the style of Robin Hood. The same kind of life is led by many an Arab or Tartar still, who as the leader of a band, acquires fame by his stirring or gallant adventures. It is not deemed dishonorable when the expeditions are directed against those out of his own tribe or nation. Jephthah's mode of life was similar to that of David when driven from the court of Saul.
jdg 11:4THE GILEADITES COVENANT WITH JEPHTHAH. (Jdg 11:4-11)
in process of time--on the return of the season.
the children of Ammon made war against Israel--Having prepared the way by the introduction of Jephthah, the sacred historian here resumes the thread of his narrative from Jdg 10:17. The Ammonites seem to have invaded the country, and active hostilities were inevitable.
jdg 11:5the elders of Gilead went to fetch Jephthah--All eyes were directed towards him as the only person possessed of the qualities requisite for the preservation of the country in this time of imminent danger; and a deputation of the chief men was despatched from the Hebrew camp at Mizpeh to solicit his services.
jdg 11:7Jephthah said, Did not ye hate me?--He gave them at first a haughty and cold reception. It is probable that he saw some of his brothers among the deputies. Jephthah was now in circumstances to make his own terms. With his former experience, he would have shown little wisdom or prudence without binding them to a clear and specific engagement to invest him with unlimited authority, the more especially as he was about to imperil his life in their cause. Although ambition might, to a certain degree, have stimulated his ready compliance, it is impossible to overlook the piety of his language, which creates a favorable impression that his roving life, in a state of social manners so different from ours, was not incompatible with habits of personal religion.
jdg 11:10the 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.
jdg 11:12HIS EMBASSY TO THE KING OF AMMON. (Jdg. 11:12-28)
Jephthah sent messengers unto the king of the children of Ammon--This first act in his judicial capacity reflects the highest credit on his character for prudence and moderation, justice and humanity. The bravest officers have always been averse to war; so Jephthah, whose courage was indisputable, resolved not only to make it clearly appear that hostilities were forced upon him, but to try measures for avoiding, if possible, an appeal to arms: and in pursuing such a course he was acting as became a leader in Israel (Deu 20:10-18).
jdg 11:13the king of Ammon . . ., Because Israel took away my land--(See on Deu 2:19). The subject of quarrel was a claim of right advanced by the Ammonite monarch to the lands which the Israelites were occupying. Jephthah's reply was clear, decisive, and unanswerable;--first, those lands were not in the possession of the Ammonites when his countrymen got them, and that they had been acquired by right of conquest from the Amorites [Jdg 11:21]; secondly, the Israelites had now, by a lapse of three hundred years of undisputed possession, established a prescriptive right to the occupation [Jdg 11:22-23]; and thirdly, having received a grant of them from the Lord, his people were entitled to maintain their right on the same principle that guided the Ammonites in receiving, from their god Chemosh, the territory they now occupied [Jdg 11:24]. This diplomatic statement, so admirable for the clearness and force of its arguments, concluded with a solemn appeal to God to maintain, by the issue of events, the cause of right and justice [Jdg 11:27].
jdg 11:28Howbeit the king of the children of Ammon hearkened not unto the words of Jephthah--His remonstrances to the aggressor were disregarded, and war being inevitable, preparations were made for a determined resistance.
jdg 11:29HIS VOW. (Jdg 11:29-31)
Then the Spirit of the Lord came upon Jephthah--The calm wisdom, sagacious forethought, and indomitable energy which he was enabled to display, were a pledge to himself and a convincing evidence to his countrymen, that he was qualified by higher resources than his own for the momentous duties of his office.
he passed over Gilead, and Manasseh--the provinces most exposed and in danger, for the purpose of levying troops, and exciting by his presence a widespread interest in the national cause. Returning to the camp at Mizpeh, he then began his march against the enemy. There he made his celebrated vow, in accordance with an ancient custom for generals at the outbreak of a war, or on the eve of a battle, to promise the god of their worship a costly oblation, or dedication of some valuable booty, in the event of victory. Vows were in common practice also among the Israelites. They were encouraged by the divine approval as emanating from a spirit of piety and gratitude; and rules were laid down in the law for regulating the performance. But it is difficult to bring Jephthah's vow within the legitimate range (see on Lev 27:28).
jdg 11:31whatsoever cometh forth of the doors of my house to meet me--This evidently points not to an animal, for that might have been a dog; which, being unclean, was unfit to be offered; but to a person, and it looks extremely as if he, from the first, contemplated a human sacrifice. Bred up as he had been, beyond the Jordan, where the Israelitish tribes, far from the tabernacle, were looser in their religious sentiments, and living latterly on the borders of a heathen country where such sacrifices were common, it is not improbable that he may have been so ignorant as to imagine that a similar immolation would be acceptable to God. His mind, engrossed with the prospect of a contest, on the issue of which the fate of his country depended, might, through the influence of superstition, consider the dedication of the object dearest to him the most likely to ensure success.
shall surely be the Lord's; and [or] I will offer it up for a burnt offering--The adoption of the latter particle, which many interpreters suggest, introduces the important alternative, that if it were a person, the dedication would be made to the service of the sanctuary; if a proper animal or thing, it would be offered on the altar.
jdg 11:32HE OVERCOMES THE AMMONITES. (Jdg 11:32-33)
Jephthah passed over unto the children of Ammon . . . and the Lord delivered them into his hands--He met and engaged them at Aroer, a town in the tribe of Gad, upon the Arnon. A decisive victory crowned the arms of Israel, and the pursuit was continued to Abel (plain of the vineyards), from south to north, over an extent of about sixty miles.
jdg 11:34Jephthah came to Mizpeh unto his house, and, behold, his daughter came out to meet him with timbrels and with dances--The return of the victors was hailed, as usual, by the joyous acclaim of a female band (Sa1 18:6), the leader of whom was Jephthah's daughter. The vow was full in his mind, and it is evident that it had not been communicated to anyone, otherwise precautions would doubtless have been taken to place another object at his door. The shriek, and other accompaniments of irrepressible grief, seem to indicate that her life was to be forfeited as a sacrifice; the nature of the sacrifice (which was abhorrent to the character of God) and distance from the tabernacle does not suffice to overturn this view, which the language and whole strain of the narrative plainly support; and although the lapse of two months might be supposed to have afforded time for reflection, and a better sense of his duty, there is but too much reason to conclude that he was impelled to the fulfilment by the dictates of a pious but unenlightened conscience.