Augustine of Hippo
It is thus recorded: Jephthah made a vow to the Lord, stating, "If you deliver the Ammonites into my hands, when I return peacefully from them, whatever comes out of the gate of my house to greet me shall belong to the Lord, and I will offer it as a burnt offering." In making this vow, Jephthah did not refer to any livestock that he could offer as a burnt offering according to the law. Additionally, it was not customary for victorious commanders returning from battle to be greeted by animals. While dogs, which are silent creatures, often rush out to welcome their masters, Jephthah did not have dogs in mind; such a vow would not only be unlawful but also regarded as contemptible and impure by the law. A sacrifice of that nature would have been offensive to the Lord.
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Furthermore, he did not say, "Whatever comes out of the gate of my house to meet me shall belong to the Lord, and I will offer it as a burnt offering." Instead, Jephthah declared, "Whatever comes out of the gate of my house towards me shall belong to the Lord, and I will offer it as a burnt offering." Thus, it is clear that from the outset, he was thinking of a person; this was likely not limited to his sole daughter, as no one else could have held greater significance in his eyes than perhaps his wife.