Judges 11:31

People imitate those who do good deeds, therefore, not out of love for these good deeds but because of their utility.… The king of Moab took note of Jephthah. But, because it was his firstborn and a human being rather than an animal that he killed, God took pity on him, since he did it in affliction and not through love. In the case of Jephthah, if it had been one of his servants who had been first to encounter him, he would have killed him. But, in order that people would not engage in the sacrifice of their fellow human beings, he caused his own daughter to meet him, so that others would be afraid, lest they offer human beings by vow to God.

SINCE ABRAHAM WAS FORBIDDEN TO SACRIFICE HIS SON, WHY WAS JEPHTHAH NOT FORBIDDEN TO CARRY OUT THE SACRIFICE OF HIS DAUGHTER? (Gen. 22:11–12; Judg. 11)? — There is a great difference between Abraham’s case and Jephthah’s case. First, Abraham was legitimately born, whereas Jephthah was illegitimate, for he was the son of a prostitute. Next, Abraham was of excellent conduct, but Jephthah was a leader of bandits. Abraham was a righteous man, proven in temptation; in Jephthah, however, there is no testimony of righteousness. Abraham, therefore, was commanded to offer his son to God so that it might be shown to people how greatly Abraham trusted God, since at His command he did not hesitate even to kill his own son. For He who, contrary to worldly hope, could cause him to be born of a barren old woman, was clearly able, contrary to worldly reasoning, to raise him from the dead (Heb. 11:19). By this act Abraham’s righteousness was increased. For God showed that He did not desire the boy’s blood, but that His servant Abraham might become greater by this deed. For He wills those who love Him to suffer something, so that His advancing them may appear just. But Jephthah, a violent and thoughtless man, in foolish devotion promised a gift to God, saying: “Whatever comes out to meet me from the doors of my house when I return from the slaughter, I will offer it to God.” Was he forced to make this vow, or did he understand how a vow ought to be made? What if a dog or a donkey had met him, which the Lord forbade to be offered? Or if someone else’s son, or his wife, so that in another’s grief he might exult that he had paid his vow? Therefore, what his careless mind had vowed to another’s ruin was, by divine judgment, turned back upon himself. And Jephthah was so senseless that he did not afterwards recognize that he had vowed foolishly, so that his error, which began with him, might be corrected by him. For he ought to have understood that God does not delight in such a sacrifice, and to have prayed for pardon for his foolishness, and offered something else that was not against the Law. Instead, he showed himself “faithful” by becoming a murderer, whereas it is clear that foolish faith not only fails to benefit, but harms. Therefore in the matter of his daughter he himself was struck down, and for this reason God took no notice of such a sacrifice. For if He had forbidden it, Jephthah would have seemed to want to offer something else to Him, although he knew that what was unworthy must not be offered. But his daughter gained by it: because she, innocent, died on account of her father’s sins, she escaped the punishment of hell, which perhaps she might not have attained by living long. And as for the triumph of Jephthah’s victory, it was not achieved by his merit nor by that of the people; for it is not written that they requested God to give them a defender. Or did the Lord send Jephthah himself, or speak to him? Rather, because the Philistines were praising their gods as those who had made the sons of Israel subject to them, and were reviling the God of Abraham, therefore, for the honor of His name, God took vengeance on the Philistines, even if not for these men’s sake, yet for Abraham’s merit and His own glory. Or shall Samson be called worthy because the Spirit of the Lord came upon him while he was consorting with prostitutes (Judg. 14:6, 19; 15:14), when this is to be understood as done for the destruction of the Philistines?

And whereas he [Jovinianus] prefers the fidelity of the father Jephthah to the tears of the virgin daughter, that corroborates our point. For we are not commending virgins of the world so much as those who are virgins for Christ's sake. Most Hebrews blame the father for the rash vow he made, "If you will indeed deliver the children of Ammon into my hand, then it shall be that whatsoever comes out of the doors of my house to meet me, when I return in peace from the children of Ammon, it shall be for the Lord's, and I will offer it up for a burnt offering." Supposing (the Hebrews say) a dog or an ass had met him, what would he have done? Their meaning is that God so ordered events that he who had improvidently made a vow should learn his error by the death of his daughter.

With these words [of his vow] at any rate Jephthah did not vow some kind of animal that he could offer as a whole burnt offering according to the law; it is neither customary now nor was it in the past that cattle would run to meet generals returning victoriously from war. As far as mute animals are concerned, dogs often run to meet their masters and sport with them in fawning servitude. But Jephthah could not have been thinking about dogs in his vow, because it would seem that he would have vowed not only something unlawful but also something contemptible and unclean according to the law. It would have been an insult to God. Nor does he say, "I will offer as a whole burnt offering whatever will come out of the doors of my house to meet me." He says, "I will sacrifice whoever comes out of my house." Thus, there can be no doubt that he was thinking of nothing else than a human being—not his only daughter, however. Yet who would have been able to surpass her in her father's eyes except perhaps his wife?