Human Sacrifice in the Bible: Judges 11:29-40

Then the spirit of the LORD came upon Jephthah. He went through Gilead and Manasseh and returned to Mizpah in Gilead and went on to Ammon. Jephthah promised the LORD: "If you will give me victory over the Ammonites, I will burn as an offering the first person that comes out of my house to meet me, when I come back from the victory. I will offer that person to you as a sacrifice." So Jephthah crossed the river to fight the Ammonites, and the LORD gave him victory. He struck at them from Aroer to the area around Minnith, twenty cities in all, and as far as Abel Keramim. There was a great slaughter, and the Ammonites were defeated by Israel. When Jephthah went back home to Mizpah, there was his daughter coming out to meet him, dancing and playing the tambourine. She was his only child. When he saw her, he tore his clothes in sorrow and said, "Oh, my daughter! You are breaking my heart! Why must it be you that causes me pain? I have made a solemn promise to the LORD, and I cannot take it back!" She told him, "If you have made a promise to the LORD, do what you said you would do to me, since the LORD has given you revenge on your enemies, the Ammonites." But she asked her father, "Do this one thing for me. Leave me alone for two months, so that I can go with my friends to wander in the mountains and grieve that I must die a virgin." He told her to go and sent her away for two months. She and her friends went up into the mountains and grieved because she was going to die unmarried and childless. After two months she came back to her father. He did what he had promised the LORD, and she died still a virgin. This was the origin of the custom in Israel that the Israelite women would go out for four days every year to grieve for the daughter of Jephthah of Gilead. -Judges 11:29-40  (GNB)

Jephthah promises God that he will "burn as an offering the first person that comes out of" his house, if he gets a victory over the Ammonites. And of course he gets his victory. The first to walk out of his home was his daughter, and in the end she is sacrificed via burning. This shows how primitive people were in the time this story was written. It also shows that the content of scripture is society based, not inspiration from God — an all-knowing god wouldn't change its mind.