Jephthah knew that human sacrifice was strictly forbidden in Isreal but his foolishness caused him to make a reckless vow. The Q is did he actually follow thru with it?
Here is one bible commantators interpretation of Judges 11;
verses 36-40;
The text does not explicitly say that he killed his daughter, only that he "carried out his vow". When the verse goes on the say that "she knew no man", some take this to mean that she was "sacrificed" by being dedicated to a life of perpetual virginity. Until the wicked reigns of Ahaz and Manasseh centuries later (2 Kings 16:3, 21:6) there is no record of human sacrifice in Isreal. The great respect that Jephthah had for God surely would have prevented him from making such a perverse offering. And the fact that Jephthah permitted his daughter to bewail her virginity (vv 37,38) for two months fits an explanation of perpetual virginity better than human sacrifice. In ancient Isreal society, the father had the power to prohibit a daughter to marry. The conjunction in Jephthah's pivotal statement in v. 31, that whatever or whoever came out of the door "shall be the LORD's, and I will offer it up as a burnt offering" could be translated or. Thus, if a person came out first, he would dedicate that person to the LORD, or if an animal came out first, he would offer the animal as a burnt sacrifice.
I have to agree with the above interpretation because although God's son was sacrificed on our behalf, God never expected humans to do such a thing with thier children. I know that Abraham and Isaac will be brought up, but that was a test of Faith only to see if Abraham would obey. God was not going to really allow Abraham to really kill Isaac and he had an animal ( a lamb) ready for the sacrifice which proves he never intended for it to be carried out.
What happened with Abraham and Isaac in the OT was to paint a "picture" pointing to the future time when Christ would be offered up as our sacrificial lamb. Abraham pictures God the father and Isaac, the son of God. Again, no actual human sacrifice was going to take place for this would have violated God's own laws. Abraham probably did not understand God's request fully at the time some say, but decided to follow the direction anyway. I personally believe Abraham knew God must have something else in mind and knew full well that whatever it was, God would reveal it to him before anything actually happened to Isaac. That is where his strong faith and full assurance on God came into play.
Peace, Lilly