A MORE COMPLETE EXPLANATION...
The Christian idea of the messiah is that Jesus was the blood sacrifice that saves everyone from his or her sin. But who, exactly, died on that cross? If it was Jesus-the-god, that would mean that Gd can die. But how can Gd die? If it was only Jesus-the-human, then all Christians are left with is a human sacrifice. What, exactly, does Gd say about human sacrifice in the TaNaKH?
In Deuteronomy, Gd calls human sacrifice something that Gd hates; an abomination to Gd.
Take heed to thyself that thou be not snared by following them, after that they be destroyed from before thee; and that thou inquire not after their gods, saying, How did these nations serve their gods? even so will I do likewise. Thou shalt not do so unto the Eternal thy Gd: for every abomination to the Eternal, which he hateth, have they done unto their gods; for even their sons and their daughters they have burnt in the fire to their gods. [Deuteronomy 12:30-31]
In Jeremiah, Gd tells us that Human sacrifice is so horrible a concept, that it did not even come into Gd's mind.
Because they have forsaken me, and have estranged this place, and have burned incense in it unto other gods, whom neither they nor their fathers have known, nor the kings of Judah, and have filled this place with the blood of innocents; They have built also the high places of Baal, to burn their sons with fire for burnt offerings unto Baal, which I commanded not, nor spoke it, neither came it into my mind: Therefore, behold, the days come, saith the Eternal, that this place shall no more be called Tophet, nor The Valley of the Son of Hinnom, but The Valley of Slaughter. [Jeremiah 19:4-6]
Similarly, in Psalm 106 and in Ezekiel 16:
Yea, they sacrificed their sons and their daughters unto devils, And shed innocent blood, even the blood of their sons and of their daughters, whom they sacrificed unto the idols of Canaan: and the land was polluted with blood. [Psalm 106:37-38]
Moreover thou hast taken thy sons and thy daughters, whom thou hast borne unto me, and these hast thou sacrificed unto them to be devoured. Is this of thy whoredoms a small matter? [Ezekiel 16:20]
Some Christians might claim that Gd seemed to want human sacrifices, because Gd appeared to demand one from Abraham, when He commanded the sacrifice of Isaac. This is a misreading of the biblical text in Genesis. When one reads this section carefully, one sees something quite different.
Most Jewish biblical commentators interpret this incident as a test of Abraham's loyalty: Gd wanted to see if he would actually kill Isaac, his own son. However, a number of Jewish commentators from the medieval era, and many in the modern era as well, read the text somewhat differently. The early rabbinic midrash 'Genesis Rabbah' imagines Gd as saying 'I never considered telling Abraham to slaughter Isaac.' Rabbi Yona Ibn Janach (Spain, 11th century) wrote that Gd demanded only a symbolic sacrifice. Rabbi Yosef Ibn Caspi (Spain, early 14th century) wrote that Abraham's imagination led him astray, making him believe that he had been commanded to sacrifice his son. Ibn Caspi writes 'How could Gd command such a revolting thing?'
Rabbi Joseph H. Hertz (Chief Rabbi of the British Empire), writes that child sacrifice was actually 'rife among the Semitic peoples,' and suggests that 'in that age, it was astounding that Abraham's Gd should have interposed to prevent the sacrifice, not that He should have asked for it.' Hertz interprets the Binding of Isaac as demonstrating that human sacrifice is abhorrent. 'Unlike the cruel heathen deities, it was the spiritual surrender alone that Gd required.'
Let's examine the text:
And it came to pass after these things, that Gd did test Abraham, and said unto him, Abraham: and he said, Behold, here I am. And he said, Take now thy son, thine only son Isaac, whom thou lovest, and get thee into the land of Moriah; and offer him there for a burnt offering upon one of the mountains which I will tell thee of. [Genesis 22:1-2]
The text reads that Abraham should 'offer him there for a burnt offering'.
It does not read that Gd told Abraham to kill him for a burnt offering!
The original Hebrew is actually even clearer on this issue. The Hebrew reads, 'v’ha-ah-ley-hu sham l’o-lah.' It translates as, 'Raise him up there FOR a sacrifice.' The text does not say that Gd demanded Isaac to BE a sacrifice, but rather only that he should be raised up for one.
Furthermore, a close reading of the text tells us that this was a test, and that Abraham did not pass it. What is the test to which Abraham is being put? Gd wants Abraham to tell Gd, 'NO! I WON’T DO IT!' Abraham had just defended people he did not know in Sodom and Gemorrah. So Gd's test of Abraham is whether or not he would defend his own family as vigorously as he had defended strangers. Like many of us, he did not. He flunked. Many of us, for example, will talk sweetly to a voice on the phone, get off the phone, and then speak disrespectfully to our kids or our spouse, treating others, even strangers, better than we treat those we love.
When the test is first put before Abraham, the day before he actually takes the knife, preparing to kill his own son, Gd speaks to him directly:
And it came to pass after these things, that Gd did tempt Abraham, and said unto him, Abraham: and he said, Behold, here I am. And He said, Take now thy son, thine only son Isaac, whom thou lovest, and get thee into the land of Moriah; and offer him there for a burnt offering upon one of the mountains which I will tell thee of. [Genesis 22:1-2]
Please not that it is Gd speaking directly to Abraham, and not an angel of Gd.
However, after he takes hold of the knife, it is only an Angel of Gd who speaks to Abraham:
And Abraham stretched forth his hand, and took the knife to slay his son. And the Angel of the Eternal called unto him out of heaven, and said, Abraham, Abraham: and he said, Here am I. [Genesis 22:10-11]
And then later it is still only an Angel of Gd who speaks to Abraham:
And the Angel of the Eternal called unto Abraham out of heaven the second time… [Genesis 22:15]
As a matter of fact, Gd never spoke directly to Abraham again. From the very moment that Abraham demonstrated his willingness to actually kill his son, Gd never again spoke directly to Abraham.
Note also that the promises of the Angel of Gd to Abraham are nothing new, they are only reiterating what Gd, directly, had already promised to him (cf. Gen. 12:2, 12:3, 12:7, 13:15, 13:16, 13:17, 15:1, 15:5, 15:7, 15:14, 15:18, 17:2, 17:4, 17:6, 17:8, 17:16). It is as if Gd was saying to the Angel, 'I am through with him. Pat him on the head because he thinks he did right, remind him of his reward for his previous faith, but I am done with him!'
You see, Gd had already told Abraham His covenant would go through Isaac. Gd wanted Abraham to say, 'Wait a minute, You, Gd, are now going against Your own word!' Gd knows that we are always closer to those we will argue with, than with those we will not.
When person does wrong, who are you more likely to admonish: someone you know, or someone you do not know?
Gd wants us to be that close to Gd. Gd wants us to be like Abraham, who was willing to argue with Gd regarding strangers in Sodom and Gemorrah. Gd wants us to be as close to Gd as Moses was, indicated by the fact that Moses argued with Gd -- repeatedly -- on behalf of the People of Israel. Gd wants us to be like Job, who felt so close to Gd that he could argue with Gd for justice. We can argue with Gd like true close friends can argue with each other, because Gd is truly our Closest Friend. Abraham flunked Gd's test, and so Gd never spoke to Abraham directly again.
Note also the true meaning of the word, 'Israel,' which is 'One who wrestles with Gd.' We are not to be blind followers (the word 'Christian' means 'follower of the Christ’), and we are not to merely submit to Gd ('Islam' means 'voluntary submission to Gd.' A Muslim is one who submits to Gd).
We Jews are to be wrestlers with Gd, like True Friends can do with each other. THAT is how close Gd wants us to be with Him.