WHATEVER comes out from the doors of my house to meet me, I will offer it up for a burnt offering

[tonychanyt]

ESV Judges 11:

30 Jephthah made a vow to the LORD and said, “If you will give the Ammonites into my hand, 31then whatever comes out from the doors of my house to meet me when I return in peace from the Ammonites shall be the LORD’s, and I will offer it up for a burnt offering.”

What did Jephthah expect to come out when he made the vow?

Brenton Septuagint Translation was more specific:

it shall come to pass that whosoever shall first come out of the door of my house to meet me when I return in peace from the children of Ammon, he shall be the Lord's: I will offer him up for a whole-burnt-offering.

Jephthah was thinking about a human sacrifice.

Keil and Delitzsch:

By the words אשׁר היּוצא, "he that goeth out," even if Jephthah did not think "only of a man, or even more definitely still of some one of his household," he certainly could not think in any case of a head of cattle, or one of his flock. "Going out of the doors of his house to meet him" is an expression that does not apply to a herd or flock driven out of the stall just at the moment of his return, or to any animal that might possibly run out to meet him. For the phrase לקראת יצא is only applied to men in the other passages in which it occurs.

Ellicott explained:

Nothing can be clearer than that the view held of this passage, from early Jewish days down to the Middle Ages, and still held by nearly all unbiased commentators, is the true one, and alone adequately explains the text: viz., that Jephthah, ignorant as he was—being a man of semi-heathen parentage, and long familiarised with heathen surroundings—contemplated a human sacrifice.

The consensus was a human sacrifice until modern times.

Pfeiffer sensibly observes (Dub. vexata, p. 356): “What kind of vow would it be if some great prince or general should say, ‘O God, if Thou wilt give me this victory, the first calf that meets me shall be Thine?’” Jephthah left God, as it were, to choose His own victim, and probably anticipated that it would be some slave.

Jephthah didn't think his own daughter would greet him first.

The notion of human sacrifice was all but universal among ancient nations, and it was specially prevalent among the Syrians, among whom Jephthah had lived for so many years, and among the Phœnicians, whose gods had been recently adopted by the Israelites (Judges 10:6). Further than this, it was the peculiar worship of the Moabites and Ammonites, against whom Jephthah was marching to battle; and one who had been a rude freebooter, in a heathen country and a lawless epoch, when constant and grave violations of the Law were daily tolerated, might well suppose in his ignorance that Jehovah would need to be propitiated by some offering as costly as those which bled on the altars of Chemosh and Moloch.

Jephthah was ignorant of Moses' Law.

The Law was one thing; the knowledge of it and the observance of it was quite another. During this period we find the Law violated again and again, even by judges like Gideon and Samson; and the tendency to violate it by human sacrifices lasted down to the far more enlightened and civilised days of Ahaz and Manasseh (2Chronicles 28:3; 2Chronicles 33:6). Indeed, we find the priests expressly sanctioning, even in the palmiest days of David’s reign, an execution which, to the vulgar, would b

Barnes, Jamieson-Fausset-Brown, Gill, and Cambridge Bible all agreed that Jephthah had a human sacrifice in mind.