I disagree. Nowhere does God ever demand or even accept a HUMAN sacrifice of His people - it was detestable to Him. It was the pagans who did such things. We have this from Scripture:
Leviticus 18:21 ESV
You shall not give any of your children to offer them to Molech, and so profane the name of your God: I am the Lord.
2 Kings 21:6 ESV
And he burned his son as an offering and used fortune-telling and omens and dealt with mediums and with necromancers. He did much evil in the sight of the Lord, provoking him to anger.
Deuteronomy 12:31 ESV
You shall not worship the Lord your God in that way, for every abominable thing that the Lord hates they have done for their gods, for they even burn their sons and their daughters in the fire to their gods.
2 Kings 3:27 ESV
Then he took his oldest son who was to reign in his place and offered him for a burnt offering on the wall. And there came great wrath against Israel. And they withdrew from him and returned to their own land.
Jeremiah 7:31 ESV
And they have built the high places of Topheth, which is in the Valley of the Son of Hinnom, to burn their sons and their daughters in the fire, which I did not command, nor did it come into my mind.
Jeremiah 32:35 ESV
They built the high places of Baal in the Valley of the Son of Hinnom, to offer up their sons and daughters to Molech, though I did not command them, nor did it enter into my mind, that they should do this abomination, to cause Judah to sin.
Psalm 106:37-41 ESV
They sacrificed their sons and their daughters to the demons; they poured out innocent blood, the blood of their sons and daughters, whom they sacrificed to the idols of Canaan, and the land was polluted with blood. Thus they became unclean by their acts, and played the whore in their deeds. Then the anger of the Lord was kindled against his people, and he abhorred his heritage; he gave them into the hand of the nations, so that those who hated them ruled over them.
Ezekiel 20:31 ESV
When you present your gifts and offer up your children in fire, you defile yourselves with all your idols to this day. And shall I be inquired of by you, O house of Israel? As I live, declares the Lord God, I will not be inquired of by you.
The only time that the Lord even suggested the offering up of a man's daughter or son was when God tested Abraham with the sacrifice of his son Isaac and then He stopped him from actually carrying it out. It was a testing of his faith. I believe it was also a foreshadowing of when Jesus Christ, the Son of God would shed His blood and die upon a cross for the sins of the world.
In all the sacrifices that the Lord commanded of His people Israel for sin offerings, it was to always be an unblemished animal and the blood was to make atonement for sin. In Leviticus He tells us that only by the shedding of blood is there atonement for sin. Until Christ came, the blood offerings of the priests of the temple were as covering for sins (expiation). When Christ died, His blood made propitiation (taken away) for all sin and His once-for-all sacrifice would never need to be repeated. When we accept that Christ died for our sins, we are cleansed and made righteous in Him. Everything God does is for a purpose.
First off, yes He does. He demands Abraham sacrifice his son. The command word He uses in the Binding of Isaac story is "olah" which means: burnt offering. That He later allows the ram to be substituted does not change the fact that He DID command a human sacrifice. You can't just pretend you don't see that.
Secondly, God isn't making any demand in the Jephthah story. Jephthah is going rogue. The word Jephthah vows is the same as God's command to Abraham: "olah".
Finally, there is no substitution in the Jephthah story.The text says that he did as he vowed. That's it. He killed her and burned he up.
You have to deal with the text as it exists. You can't add, subtract or ignore elements to fit your desires. When people try to whitewash this story, they wind up missing the whole point. Jephthah wasn't trying to please God. Jephthah was trying to be God.