Though Christians don't perform animal sacrifice, those under the Old Testament certainly did. And so, since Christianity is an extension of that Old Testament Judaism, Christians do advocate such animal sacrifice, sort of “by association.” But we might say that the slaughter of innocent animals seems particularly un-Christian and cruel. How does Christianity go together with a religion that practised animal sacrifice, and a God who commanded it?
It should be noticed, first of all, that the practice of animal sacrifice dates back to the very beginning of the fall of man. In Genesis 4 we see Abel sacrificing from his flock of sheep; which the book of Hebrews calls “a more acceptable sacrifice than Cain”, who offered “of the fruit of the ground.” Even prior to this event, when Adam and Eve sinned, God Himself made them “garments of skins”, implying the sacrifice of an animal. So from the time of Adam and Eve, animal sacrifice was ordained by God. We also see, for example, that Noah made sacrifices of animals as well. The Israelites were not doing something new when they incorporated animal sacrifice into their worship, but were continuing on in the manner of worship that God had always required.
But why would God desire such a bloodthirsty practice? Why should innocent animals suffer? Well, the fact that the animals are innocent is precisely the point. When a sinner sins, they must pay for that sin. But the sacrificed animal pays for that sin in the place of the sinner. The animal receives what the sinner deserves. The sacrifice had to be innocent, otherwise the animal cannot be a substitute – it would have its own “sins” to pay for. But animals are not sinful. The message of the sacrificial system is that we, sinners, deserve the fate of those animals. The animals, as one's substitute, suffered what was due to the sinner. The scene of the temple altar would have been very graphic! The message would have been all the more clearly understood by those who attended.
All of this ultimately pointed to Christ. John the Baptist, when he saw Jesus coming toward him, said “Behold, the Lamb of God, who takes away the sin of the world!” (John 1:29). Animals were not a perfect sacrifice. Though innocent, they were still affected by the fall. But Jesus Christ was the perfect sacrifice. He was a sinless man. If animals were innocent, how much more was Christ!? If animals were undeserving of death, how much more was Christ? If considering the suffering of an animal helps us to realise what our fate ought to be for our sins, how much more as we consider the suffering of Christ? Animals covered a person's sin for a while, but then another sacrifice had to be made. But Jesus Christ's sacrifice is “once for all”.
Sacrificing an animal was an act of faith. There is nothing intrinsically sin-cleansing about killing an animal. In fact, sacrifices made apart from faith were despised by God. You couldn't just commit as many sins as you wanted and then think, “It's okay; we'll have a barbecue and all will be well.” It was faith in what the sacrifice meant that God honoured. But now, the true sacrifice of Christ has taken place. Animal sacrifices were an illustration of what was to come; the one true sacrifice which would be able to atone for sins. And likewise, faith in the sacrifice of Christ is necessary.
Now, in Genesis 22, Abraham is asked to sacrifice his only son, Isaac. I just want to make a few comments on this episode in the Bible, since it does seem disturbing that God would ask for a human sacrifice. But Abraham was prepared to sacrifice his son, having the faith (according to Hebrews 11:19) to believe that God would resurrect Isaac. However, God stops Abraham and provides a ram for a sacrifice instead. Again we see the substitute for the fate deserved by the sinner; Isaac in this case. When Abraham was asked to sacrifice Isaac, it probably didn't make much sense to him, since he knew his son was a sinner. This sacrifice would not atone for anything. The sacrifice of the innocent ram does make sense as an atonement. But Genesis 22:1 tells us that Abraham was being tested. (And Hebrews 11:17 reminds us of this as well.) Abraham was prepared to do this even though it didn't make sense for a number of reasons; the least of which is that human sacrifice itself doesn't make sense. What this incident is really all about is that our attempts to atone for our own sin will be rejected by God. Isaac could not be a sacrifice – there needed to be a substitute, provided by God. It also demonstrates Abraham's faith in the resurrection. According to Hebrews 11:19, Abraham received Isaac back from the dead, figuratively speaking. That is, the whole incident was supposed to teach us that through the substitutionary atonement, we will return from the dead in resurrection. Sometimes things God asks us to do won't make sense until the whole story has unfolded. In fact, much of the Mosaic Law didn't really make perfect sense until after the death and resurrection of Christ.
Finally, the Bible is clear in many places that human sacrifice is not approved of by God. Consider, for example, Deuteronomy 12:31. “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.” But there is the case of Jephthah in Judges 11 who appears to have sacrificed his daughter. There is some debate as to whether Jephthah actually sacrificed her in the sense of literally killing her on an altar, but I'm one who believes that he did. But that doesn't mean that this act is approved of by God, either. The whole of the book of Judges is really all about the phenomenal failures of Israel at that time, and this story is characteristic of the kinds of things that they did terribly wrong, when “everyone did what was right in his own eyes” (Judges 21:25).
And Samuel said, “Has the LORD as great delight in burnt offerings and sacrifices, as in obeying the voice of the LORD? Behold, to obey is better than sacrifice, and to listen than the fat of rams.” (1 Samuel 15:22)