29 Then the Spirit of the Lord came upon Jephthah, and he passed through Gilead and Manasseh, and passed through Mizpah of Gilead; and from Mizpah of Gilead he advanced toward the people of Ammon. 30 And Jephthah made a vow to the Lord…
Let’s stop there for a moment and note that all of the things in this list were done by Jephthah under the influence of the Spirit. There is no indication that he was acting rashly or speaking foolishly.
30 And Jephthah made a vow to the Lord, and said, “If You will indeed deliver the people of Ammon into my hands, 31 then it will be that whatever comes out of the doors of my house to meet me, when I return in peace from the people of Ammon, shall surely be the Lord’s, and I will offer it up as a burnt offering.”
And there we have the muffed translation. “Burnt offering” would be more accurately rendered “ascension offering.” Although at some places in Scripture, ascension offerings were burnt offerings, the word does not necessarily imply burning. Other sacrifices were burnt, but the special thing about the ascension offering was that it was given wholly to Yahweh. Nobody else got a portion; it all went straight up to the Lord. So Jephthah isn’t vowing to burn anything, he’s vowing to entirely dedicate something to God. Joel Garver writes, “‘I will offer up as a burnt offering’ could as easily be translated as ‘I will send up as something sent up,’ that is, up to the tabernacle.” 
32 So Jephthah advanced toward the people of Ammon to fight against them, and the Lord delivered them into his hands. 33 And he defeated them from Aroer as far as Minnith—twenty cities—and to Abel Keramim, with a very great slaughter. Thus the people of Ammon were subdued before the children of Israel.
34 When Jephthah came to his house at Mizpah, there was his daughter, coming out to meet him with timbrels and dancing; and she was his only child. Besides her he had neither son nor daughter. 35 And it came to pass, when he saw her, that he tore his clothes, and said, “Alas, my daughter! You have brought me very low! You are among those who trouble me! For I have given my word to the Lord, and I cannot go back on it.”
36 So she said to him, “My father, if you have given your word to the Lord, do to me according to what has gone out of your mouth, because the Lord has avenged you of your enemies, the people of Ammon.” 37 Then she said to her father, “Let this thing be done for me: let me alone for two months, that I may go and wander on the mountains and bewail my virginity, my friends and I.”
38 So he said, “Go.” And he sent her away for two months; and she went with her friends, and bewailed her virginity on the mountains. 39 And it was so at the end of two months that she returned to her father, and he carried out his vow with her which he had vowed. She knew no man.
Notice it doesn’t say she was dead, it just says she was a virgin.
And it became a custom in Israel 40 that the daughters of Israel went four days each year to lament the daughter of Jephthah the Gileadite.
OK…that was a fairly long journey to get to the main point: perpetual virginity is something to be grieved. To face the rest of her life without hope of being a wife or mother was simply devastating to Jephthah’s daughter. And key to her grieving was the presence of her friends, who grieved with her, “weeping with those who weep.”
Unfortunately, there are few in the church today who consider perpetual virginity all that big a deal, and fewer still who are willing to enter into the grief of unmarried women. For Jephthah’s daughter, the future was clear—she would never share a man’s bed or tuck his children into theirs. Perhaps that decisive clarity helped her to put a time limit on her grief. But there is no such clear answer for most unmarried women, so as hope waxes and wanes, grief continues to come in occasional waves. Of course singles must not allow this grief to characterize their whole lives, but nor should they be made to feel that they’ve sinned if they ask for a shoulder to cry on every once in a while. (Not a perpetual pity party, mind you.) The church is much too quick to start firing the contentment gun. If “Be content!” is the trigger-happy response to every mention of sadness or hurt or need, it sounds a lot like “Shut up, because I don’t want to have to care.”
1) Recognize that unwanted protracted celibacy is suffering, and weep with those who weep over that particular suffering.
2) Keep the contentment gun in its holster.
 While I can’t remember where I first heard this passage explained, the most succinct list of arguments I’ve found in favor of this reading came from Dr. Joel Garver. This list originally appeared on a private discussion list. I have used it with the author’s permission, and have shortened and slightly edited it for smoother readability:
- Jephthah’s vow was not a rash vow.
- The vow was made in the power of the Spirit of Yahweh (Judges 11:29-30; the phrases are all connected by a series of “ands”).
- The vow is thus to be taken as a prophetic judgment by an empowered judge of Israel (Judges 3:10; 6:34; etc.; Numbers 11:24-29).
- Vow-taking in general seems appropriate (Genesis 28:18-22; 31:11-13; 1 Samuel 1:11).
- Vow-taking before battle seems appropriate (Numbers 21:1-3).
- Jephthah was a man of faith (Judges 11:9, 11, 21, 27, 29; 1 Samuel 12:11; Hebrews 11:32).
- Jephthah was not a rash man, as seen in his negotiations (Judges 11:7-10; 12-28).
- Jephthah knew the law (Judges 11:12-27 and Numbers 20-21).
- Jephthah went on to serve as a judge for six more years despite the vow (Judges 12:7).
- The vow implies tabernacle service, not human sacrifice.
- The vow does seem to envisage a human coming “to meet” Jephthah from his “doors.”
- Human sacrifice was forbidden (Genesis 22; Leviticus 18:21; 20:2-5; Deuteronomy 12:31; 18:10).
- There is no other indication of human sacrifice in Israel prior to the reigns of Ahaz and Manasseh (2 Kings 16:3; 21:6) and those are offered to idols, not Yahweh.
- Priests and public opinion wouldn’t have allowed literal sacrifice, especially after two months of public mourning in which to put a stop to it (1 Samuel 14:24, 43-45).
- The essence of the vow was for the person to be “to Yahweh” (Leviticus 27:2 and Judges 11:31)
- “I will offer up as a burnt offering” could as easily be translated as “I will send up as something sent up,” that is, up to the tabernacle.
- People were “vowed” to tabernacle service (Numbers 8:14-19; Leviticus 27:1-8; possibly Judges 21:20-24; 1 Samuel 1:11; 2 Samuel 15:8; Psalm 116:14-18).
- People were vowed to the tabernacle parallel to animal offerings. The description of people vowed to the tabernacle in Leviticus 27:1-8 is precisely parallel to the description of animals vowed as offerings in Leviticus 27:9-13.
- The bringing of Samuel to the tabernacle is paralleled with the offering of bulls (1 Samuel 1:24-28).
- The firstborn of Israel—animal and human—belonged to God (Exodus 13:11-15), which meant sacrifice for animals, but religious service for humans (Exodus 24:5; Numbers 8:13-18).
- The firstborn of Israel were replaced by the Levites with their perpetual tabernacle service (Numbers 8:13-18) and sacrificial terminology (“wave offering”) could be applied metaphorically to the Levites.
- Women “served” at the tabernacle as consecrated virgins. Exodus 38:8 speaks of women who served at the tabernacle.
- Their hand-mirrors were used to make the laver of cleansing. This could symbolize their giving up any concern for personal glory or marriage and thus a commitment to celibacy
- 1 Samuel 2:22 again mentions these women.
- Eli’s sons sin by “laying with” these women. The aggravated nature of this sin might lie in part in that these women were (to remain) virgins.
- The violation of the women is connected to the theft of the Ark and the rape of Israel.
- Judges 21 speaks of the “daughters of Shiloh” where the tabernacle was. These “daughters” are engaged as a group in leading festival worship at the Feast of Booths, thereby indicating a special connection with the tabernacle. They are assumed to be unmarried virgins simply in virtue of being “daughters of Shiloh” (unlike the singling out of “virgins” from non-virgins in 21:11-12).
- Jephthah’s daughter bewails her virginity. If she were to die, she would have mourned her death.
- She assumed it was a matter of virginity simply at the mention of being “vowed” to Yahweh.
- The fulfillment of the vow is explained as “she knew no man” (Judges 11:39).
Other posts in this series (I’ll add links as I post them):
Part 6: He Sets the Lonely in Families