Summary: After the death of Avimelech, the Jewish people experience 44 years of calm until a new cycle of idol worship triggered a war with the Ammonites. Although unpopular, the people chose the Gileadite warrior Yiftach to successfully lead them against their enemy. Tragically, following their victory civil war breaks out with the Tribe of Ephraim.
A deeper look: Prior to battle, Yiftach made a vow that should God facilitate victory over the Ammonites, on his return home he would take whatever emerged from his house and sanctify it to God as an elevation offering. There is a precedent for taking a vow in times of need or danger with the intent of eliciting God’s help, just as Jacob did on his way to Lavan’s house (Genesis 28:20-22). Nevertheless, Yiftach acted inappropriately by vowing to make an offering out of ‘whatever emerged from his house’ (Taanit 4a). The impropriety of his vow was realised when on returning home, his daughter rushed out dancing in celebration (Judges 11:34).
Yiftach was a righteous and mighty man, but it is clear that he did not know the legal position of what had happened and assumed that his vow stood. Most commentators understand that since human sacrifice is forbidden, his daughter was not offered up but remained celibate, secluding herself away for the rest of her life. Disturbingly, others explain that Yiftach thought that the vow of a king is binding even if it results in the death of a human (Ramban and Rabbeinu Bachaya on Vayikra 27:29).
The Midrash relates that the legal position could have been clarified had Yiftach spoken to sage and prophet Pinchas, for even if the vow had been effective it could have been annulled. Yet tragically, Yiftach felt that as judge and ruler it was beneath him to travel to see Pinchas to resolve matters. Similarly, Pinchas did not want to denigrate his position as a prophet and high priest and refused to visit Yiftach. The two never met and were both punished for their obstinacy (Leviticus Rabbah 37:4). Another Midrash cites Yiftach as a paradigm of what can happen when an unlearned person wants to do the right thing but fails to seek Jewish legal advice from a Torah scholar (Tanchuma Bechukotai 7).