Judges 11:36

The remaining sacrifices, of which those relating to the law are a symbol, are akin to this sacrifice. But in addition, the other sacrifices akin to this sacrifice seem to me to be the shedding of the blood of the noble martyrs. It was not in vain that the disciple John saw them standing beside the heavenly altar. "But who is wise, that he shall understand these things? Or intelligent, and he shall know them?"3Now comprehend, even if to a limited extent, the more spiritual sense of such sacrifices which cleanse those for whom they are offered; one must understand the sense of the sacrifice of the daughter of Jephthah who was offered as a burnt offering because of the vow of him who conquered the children of Ammon. She who was offered as a burnt offering consented to this vow, for, when her father said, "I have opened my mouth to the Lord against you," she said to him, "And if you have opened your mouth to the Lord against me, perform your vow."
Such accounts give an appearance of great cruelty to God to whom such sacrifices are offered for humanity's salvation. We need a generous and perceptive spirit in order to refute the reproaches made against providence and, at the same time, to make a defense of all the sacrifices insofar as they are rather mysterious and beyond human nature.

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?