Shofetim 11:30

30 And Yiftach vowed a neder unto Hashem, and said, If thou shalt without fail deliver the Bnei Ammon into mine hands,

Shofetim 11:30 Meaning and Commentary

Judges 11:30

And Jephthah vowed a vow unto the Lord
Before he set out for the land of the children of Ammon, and to fight with them; hoping that such a religious disposition of mind would be regarded by the Lord, and be acceptable to him, and he should be blessed with success in his enterprise:

and said, if thou shall without fail deliver the children of Ammon into
mine hands;
though he was assured of the justness of his cause, and of his call to engage in it, he seems to have some little diffidence in his mind about the success of it; at least, was not fully certain of it.

Shofetim 11:30 In-Context

28 Howbeit the melech Bnei Ammon paid heed not unto the words of Yiftach which he sent him.

29 Then the Ruach Hashem came upon Yiftach, and he passed over Gil‘ad, and Menasheh, passed over Mitzpeh of Gil‘ad, and from Mitzpeh of Gil‘ad he passed over unto the Bnei Ammon.

30 And Yiftach vowed a neder unto Hashem, and said, If thou shalt without fail deliver the Bnei Ammon into mine hands,

31 Then it shall be, that whatsoever cometh forth of the delet of my bais to meet me, when I return b’shalom from the Bnei Ammon, shall surely be Hashem’s, and I will offer it up for an olah.

32 So Yiftach passed over unto the Bnei Ammon to fight against them; and Hashem delivered them into his hands.