In perusing questions that atheists pose to Christians to supposedly trip them up and prove that "if" there is a God, He is a horrible one, they say that He demands human sacrifice. This is blatantly untrue. The case they are speaking about is the story of Jephthah. The story can be found in Judges 11.
"Now Jephthah the Gileadite was a mighty man of valour, and he was the son of an harlot: and Gilead begat Jephthah. And Gilead's wife bare him sons; and his wife's sons grew up, and they thrust out Jephthah, and said unto him, Thou shalt not inherit in our father's house; for thou art the son of a strange woman. Then Jephthah fled from his brethren, and dwelt in the land of Tob: and there were gathered vain men to Jephthah, and went out with him. And it came to pass in process of time, that the children of Ammon made war against Israel. And it was so, that when the children of Ammon made war against Israel, the elders of Gilead went to fetch Jephthah out of the land of Tob: And they said unto Jephthah, Come, and be our captain, that we may fight with the children of Ammon. And Jephthah said unto the elders of Gilead, Did not ye hate me, and expel me out of my father's house? and why are ye come unto me now when ye are in distress? And the elders of Gilead said unto Jephthah, Therefore we turn again to thee now, that thou mayest go with us, and fight against the children of Ammon, and be our head over all the inhabitants of Gilead. And Jephthah said unto the elders of Gilead, If ye bring me home again to fight against the children of Ammon, and the LORD deliver them before me, shall I be your head? And the elders of Gilead said unto Jephthah, The LORD be witness between us, if we do not so according to thy words. Then Jephthah went with the elders of Gilead, and the people made him head and captain over them: and Jephthah uttered all his words before the LORD in Mizpeh. And Jephthah sent messengers unto the king of the children of Ammon, saying, What hast thou to do with me, that thou art come against me to fight in my land? And the king of the children of Ammon answered unto the messengers of Jephthah, Because Israel took away my land, when they came up out of Egypt, from Arnon even unto Jabbok, and unto Jordan: now therefore restore those lands again peaceably. And Jephthah sent messengers again unto the king of the children of Ammon: And said unto him, Thus saith Jephthah, Israel took not away the land of Moab, nor the land of the children of Ammon: But when Israel came up from Egypt, and walked through the wilderness unto the Red sea, and came to Kadesh; Then Israel sent messengers unto the king of Edom, saying, Let me, I pray thee, pass through thy land: but the king of Edom would not hearken thereto. And in like manner they sent unto the king of Moab: but he would not consent: and Israel abode in Kadesh. Then they went along through the wilderness, and compassed the land of Edom, and the land of Moab, and came by the east side of the land of Moab, and pitched on the other side of Arnon, but came not within the border of Moab: for Arnon was the border of Moab. And Israel sent messengers unto Sihon king of the Amorites, the king of Heshbon; and Israel said unto him, Let us pass, we pray thee, through thy land into my place. But Sihon trusted not Israel to pass through his coast: but Sihon gathered all his people together, and pitched in Jahaz, and fought against Israel. And the LORD God of Israel delivered Sihon and all his people into the hand of Israel, and they smote them: so Israel possessed all the land of the Amorites, the inhabitants of that country. And they possessed all the coasts of the Amorites, from Arnon even unto Jabbok, and from the wilderness even unto Jordan. So now the LORD God of Israel hath dispossessed the Amorites from before his people Israel, and shouldest thou possess it? Wilt not thou possess that which Chemosh thy god giveth thee to possess? So whomsoever the LORD our God shall drive out from before us, them will we possess. And now art thou any thing better than Balak the son of Zippor, king of Moab? did he ever strive against Israel, or did he ever fight against them, While Israel dwelt in Heshbon and her towns, and in Aroer and her towns, and in all the cities that be along by the coasts of Arnon, three hundred years? why therefore did ye not recover them within that time? Wherefore I have not sinned against thee, but thou doest me wrong to war against me: the LORD the Judge be judge this day between the children of Israel and the children of Ammon. Howbeit the king of the children of Ammon hearkened not unto the words of Jephthah which he sent him. Then the Spirit of the LORD came upon Jephthah, and he passed over Gilead, and Manasseh, and passed over Mizpeh of Gilead, and from Mizpeh of Gilead he passed over unto the children of Ammon. And Jephthah vowed a vow unto the LORD, and said, If thou shalt without fail deliver the children of Ammon into mine hands, Then it shall be, that whatsoever cometh forth of the doors of my house to meet me, when I return in peace from the children of Ammon, shall surely be the LORD's, and I will offer it up for a burnt offering. So Jephthah passed over unto the children of Ammon to fight against them; and the LORD delivered them into his hands. And he smote them from Aroer, even till thou come to Minnith, even twenty cities, and unto the plain of the vineyards, with a very great slaughter. Thus the children of Ammon were subdued before the children of Israel. And Jephthah came to Mizpeh unto his house, and, behold, his daughter came out to meet him with timbrels and with dances: and she was his only child; beside her he had neither son nor daughter. And it came to pass, when he saw her, that he rent his clothes, and said, Alas, my daughter! thou hast brought me very low, and thou art one of them that trouble me: for I have opened my mouth unto the LORD, and I cannot go back. And she said unto him, My father, if thou hast opened thy mouth unto the LORD, do to me according to that which hath proceeded out of thy mouth; forasmuch as the LORD hath taken vengeance for thee of thine enemies, even of the children of Ammon. And she said unto her father, Let this thing be done for me: let me alone two months, that I may go up and down upon the mountains, and bewail my virginity, I and my fellows. And he said, Go. And he sent her away for two months: and she went with her companions, and bewailed her virginity upon the mountains. And it came to pass at the end of two months, that she returned unto her father, who did with her according to his vow which he had vowed: and she knew no man. And it was a custom in Israel, that the daughters of Israel went yearly to lament the daughter of Jephthah the Gileadite four days in a year."
From this story we see that Jephthah had made a vow to God that if He delivered the Ammonites into Jephthah's hand, he would offer, as a burnt offering to the Lord, the first thing that ran out to meet him upon his return. Unfortunately for Jephthah, and even more for his daughter, it was his daughter who ran out to meet him. It is apparent that Jephthah expected a pet or one of the farm animals to run out, as this is probably what usually happened when he came home from somewhere. This time though, he was returning from war and his daughter was probably very worried about him and watching for his return to know that he was safe. When Jephthah saw that it was his daughter, he was beside himself with grief. Not only was she a beloved daughter, but she was his only child and an unmarried virgin. As such, with her death there would be no continuation of his line, which was extremely important to people back then. So why would God allow such a terrible thing as a human sacrifice? The reason the story is included in Scripture is to teach us the seriousness of making a vow to God.
Numbers 30:1-2 "And Moses spake unto the heads of the tribes concerning the children of Israel, saying, This is the thing which the LORD hath commanded. If a man vow a vow unto the LORD, or swear an oath to bind his soul with a bond; he shall not break his word, he shall do according to all that proceedeth out of his mouth."
Leviticus 27: 28-29 "Notwithstanding no devoted thing, that a man shall devote unto the LORD of all that he hath, both of man and beast, and of the field of his possession, shall be sold or redeemed: every devoted thing is most holy unto the LORD. None devoted, which shall be devoted of men, shall be redeemed; but shall surely be put to death."
When someone makes a vow, and in this case it was a vow to devote something to the Lord which doubles the necessity of fulfilling the vow, one has to keep it. Jephthah spoke rashly without considering the consequences, which we all do at some time or another. He did not stop to consider what the consequences of his vow could possibly be, as he was focused on getting what he wanted at the time, winning the war. His rash act cost him the life of his daughter and the hope of posterity.
Did God require a human sacrifice? God has never asked for a human sacrifice except of Abraham when he asked him to offer Isaac. But we know that God never intended to allow Abraham to actually slay Isaac. It was merely a test of faithfulness. God will often test us to see how far we are willing to follow Him, but when He sees our commitment He does not require the carrying out of what He has asked. The intent of our hearts is enough to please Him. Had Jephthah thought of the rashness of his vow before returning home, and realizing the possibility of something terrible coming from his rashness, he could have repented and asked God to make sure that whatever ran out to meet him was not a person, but an animal that would serve well as a sacrifice. He could not renege on his vow, as God had commanded that any vow be carried out. To allow him to not carry it out would make God a liar, which He cannot be, so the vow had to be fulfilled. But had he repented, I am sure that God would have answered his prayer and provided an animal, as God does not want or approve of human sacrifice. It is an abomination to him.
Deuteronomy 18:10 "There shall not be found among you any one that maketh his son or his daughter to pass through the fire, or that useth divination, or an observer of times, or an enchanter, or a witch."
2 Kings 17:17 "And they caused their sons and their daughters to pass through the fire, and used divination and enchantments, and sold themselves to do evil in the sight of the LORD, to provoke him to anger."
2 Kings 21:6 "And he made his son pass through the fire, and observed times, and used enchantments, and dealt with familiar spirits and wizards: he wrought much wickedness in the sight of the LORD, to provoke him to anger."
2 Kings 23:10 "And he defiled Topheth, which is in the valley of the children of Hinnom, that no man might make his son or his daughter to pass through the fire to Molech."
2 Chronicles 33:6 "And he caused his children to pass through the fire in the valley of the son of Hinnom: also he observe3d times, and used enchantments, and used witchcraft, and dealt with a familiar spirit, and with wizards: he wrought much evil in the sight of the LORD, to provoke him to anger."
In each of these verses we see that God considers people offering up their children as a burnt human sacrifice (which is what"passing through the fire" means) as wickedness that provokes His anger. He would never condone it, but in this case He had to stand back and allow it, as He could not break His own Word. It must have been as painful for the Lord, as it was for Jephthah and his daughter. The lesson to us is to not make rash vows and to carefully consider what we say and do. That is why God allowed this story to be told, in spite of the fact that it was an act that He would never find acceptable. God is bound by His own words, which is why we can believe and count on Him to be faithful and true. It is this very quality which allows us to be able to trust in Him.
So we see that this was not a matter of God being a God who demands or even condones human sacrifice, but One who is faithful to keep His word no matter what the cost.