(Today's passage covers a few minor judges and the story of Jephthah, who defeats the Ammonites, sacrifices his own daughter, and murder 42,000 Ephraimites.)
Everyone knows the story of Abraham's "sacrifice" of Isaac. (Gen. 22) That time, God stepped in at the last minute to save Isaac, Abraham's only son by his wife Sarah. In that story, we have an example of God's mercy, his reward to a faithful parent.
Things turn out differently in Judges 11.
A bit of backstory: the Israelites have fallen to corruption (yes, again), and the Gileadites east of the Jordan have been conquered by the children of Ammon. (Judg. 10) They turn to Jephthah, the exiled son of a prostitute, and his band of adventurers (NIV, "vain men"in the KJV) to rid them of their latest oppressors. Jephthah milks this deal for all its worth, getting a promise from the Gilead elders that he will be their ruler if he rids them of the Ammonites. (Judg. 11:1-11)
Jephtah then has a long parley with the king of the Ammonites, trying to establish who has rightful claim to the land. (Judg. 11:12-28) In the end, the issue is undecided and Jephthah's forces go to war with the Ammonites.
Just before the battle, Jephtah makes his big mistake. He makes a solemn vow with God that if he defeats the Ammonites, he will sacrifice the first thing that comes out of his doors to greet him when he goes home. (Judg. 11:29-31)
I'm sure we can all see where this is going.
Jephtah conquers the 20 Ammonite cities, ousts them from Gilead, and goes home to find his daughter, his only child, coming out to greet him. (Judg. 11:32-34) Though his daughter is dancing and singing, Jephthah tears his clothes and bewails his oath. But, in the end, an oath to God is unbreakable, and he can't retract it.
Jephthah's daughter -- who remains unnamed -- understands her father's position and agrees to be a sacrifice for her father. She asks only for two months to go into the mountains and mourn, because she will die a virgin. This accomplished, she comes home and is sacrificed for God. (Judg. 11:36-39) God does not step in at the last minute to say, "Jephthah, don't do it!" as he did for Abraham. Here, the sacrifice is given and (we assume) accepted at face value.
This is especially horrid because in the Pentateuch, God expressly forbid child sacrifice. (See, for example, Lev. 18:21, Deut. 12:31, and Deut. 18:10) It may be that even though Jephthah judged Israel for six years (Judg. 12:7), even he had become corrupted by the surrounding pagan tribes. True, he had not intended to sacrifice his daughter, but when he found out it was required, he didn't shirk from his duties. This whole incident forces us to ask, "where is the God that stopped Abraham from doing this, and why didn't he stop Jephthah?"