"30 And Jephthah made a vow to the LORD : "If you give the Ammonites into my hands, 31 whatever comes out of the door of my house to meet me when I return in triumph from the Ammonites will be the LORD's, and I will sacrifice it as a burnt offering."
And of course as Jephthah returns from the Ammonites in victory, who is it that first comes out of his house to greet him but his daughter. At first when I would read this I was thinking "well what did he expect come out of his house? The cat? a beach ball?" But of course this is part of how the LORD works mysteriously. Now I ask you to suspend your amazement at the willingness of Biblical children to be burnt sacrifices for just a moment, as this is actually what happens. Jephthah's daughter consents to being a burnt offering on the condition that she may go into the mountains with her friends and mourn for a while. Jephthah grants her request. One of the weirder aspects of this story is found at the end of chapter 11 where in verse 39 and 40 it says "39 After the two months, she returned to her father and he did to her as he had vowed. And she was a virgin.
From this comes the Israelite custom 40 that each year the young women of Israel go out for four days to commemorate the daughter of Jephthah the Gileadite."
From what I can tell, and from every biblical scholar I have spoken too, and even in the liner notes in my bible, this is the only place in the bible that this four day festival is mentioned, which many people take as meaning that it must have been a local village festival. I have a different theory about it. If we can now skip ahead to the end of Judges we find that the Benjamites have greatly sinned against God and the rest of Israel (although it seems the rest of Israel isn't doing so good either...) so the Isrealites practically anihalated the Benjamites (save maybe six hundred who ran away) and then swore an oath not to give any of their daughters in marriage to them. The LORD at this point decides that he doesn't want one of the 12 tribes to be wiped out so they decide to go hide in a vinyard and wait for some girls to show up celebrating a festival. In 21:18-22 it says "18 We can't give them our daughters as wives, since we Israelites have taken this oath: 'Cursed be anyone who gives a wife to a Benjamite.' 19 But look, there is the annual festival of the LORD in Shiloh, to the north of Bethel, and east of the road that goes from Bethel to Shechem, and to the south of Lebonah."
20 So they instructed the Benjamites, saying, "Go and hide in the vineyards 21 and watch. When the girls of Shiloh come out to join in the dancing, then rush from the vineyards and each of you seize a wife from the girls of Shiloh and go to the land of Benjamin. 22 When their fathers or brothers complain to us, we will say to them, 'Do us a kindness by helping them, because we did not get wives for them during the war, and you are innocent, since you did not give your daughters to them.' "
I present to you that this is the same festival previously mentioned in Judges 11. I present to you that the LORD caused Jephthah to swear a careless oath and fullfill it so that this anual festival would take place so that one of the 12 would not be obliterated. I would also like to point out that this happening directly impacts the crowning of Israels first king as Saul was a Benjamite. The fact that the fathers of the daughters who were married off to the remaining Benjamites were so angry could also explain why the festival is never mentioned again throughout the Bible. Kind of a "well if this is whats going to happen then screw it!" sort of attitude. Thus, the LORD works in mysterious ways, and a "WTF!?" type story all of a sudden kind of makes sense.