Whether Jephthah’s daughter was sacrificed as a burnt offering or just remained unmarried for the rest of her life, is a perennial dilemma in the exegesis, with emotions attached to either view. It also makes a substantial difference in how to tell the story. What is the argument for the burnt offering in the text? Jephthah had said: I will offer it up for a burnt offering
(Judges 11:31), and here it says that he did with her according to his vow.
In the days of the Old Testament, a human sacrifice is not by far as unthinkable as it is now.
The idea that the daughter was not burnt only arose many centuries later, about 1200 AD.
If it were about remaining unmarried only, Jephthah’s lament in verse 35 sounds rather exaggerated. The same applies to the passage as a whole (Judges 11:34–40).
The concept of ceremonious dedication to the Lord for life (which is implied in the other view) was unknown to Israel, Samson and Samuel being unique cases.
39 And at the end of two months, she returned to her father, who did with her according to his vow that he had made. She had never known a man, and it became a custom in Israel