God told them to do it.

That is what the student has to assume because of later revelation.

We also for example in reference to the fall, assume that either God told Eve "neither shall you touch it." Since there is no record of God forbidding "touching" the tree of the knowledge of good and evil. We assume either Eve was commanded by God to not touch the fruit, or Adam forbade touching. Because any other observation other than this assumption makes sin existent in Eve before the eating, thru lying.

Thus we can assume that animal sacrifice was introduced to them but God chose not to give the details about it. Keep in mind that from Eden to the flood and Babel there was a tremendous amount of world activity. But God limits our exposure to this time period to just 11 chapters.

The necessity of blood was a lesson soon learned by the sons of the first human couple. The time came for both Abel and Cain to bring their sacrifices before God (Gen. 4:3-16). Cain offered for sacrifice the fruit of his labors in the field. The offering was vegetable, and it was bloodless. Abel brought a blood-offering taken from his flock. When God passed judgment on the two types of offerings, that of Cain was rejected, and that of Abel was accepted. So a lesson was taught: One cannot approach God by whatever means one chooses. It is man who sinned and offended the holy God; it is God who must do the forgiving. Therefore, it is not for man to choose the means of forgiveness, but for God, and God has chosen the means to be blood. Cain had chosen to approach God in his own way, but he was rejected. Abel chose the way God demanded, and his sacrifice was accepted.

As biblical history develops in the Book of Genesis, we find that all the ones with whom God was pleased came to Him by means of blood. Noah immediately offered up blood sacrifices when he left the ark. He was followed by other great men in Jewish history: Abraham, Isaac, and Jacob, all of whom were careful to approach God by means of blood. When Moses received the Law at Mount Sinai, the redemptive element of blood ran throughout the entire Law with its 613 commandments.

A great summary statement for the entire Law is found in The Third Book of Moses, Leviticus 17:11: For the life of the flesh is in the blood; and I have given it to you upon the altar to make atonement for your souls: for it is the blood that makes atonement by reason of the life. It can easily be said that all of the Law revolves around this one statement. There were commandments which God gave in the Law that were to be obeyed. Disobedience was sin. If disobedience did take place, the means of atonement for the sin was blood. The Book of Leviticus opens by giving great detail to the different types of blood-sacrifices. All of these different sacrifices had the same purpose: that the Jew might be rightly related to God.

All seven feasts of Israel: Passover, Unleavened Bread, Firstfruits, Pentecost, Trumpets, Day of Atonement, and Tabernacles required the shedding of blood. The Yom Kippur or Day of Atonement ceremony was greatly detailed in Leviticus 16, where careful instructions are given for the shedding of blood to atone for the sins of the Jewish nation. The Tabernacle and the Temple both were built to expedite and to make efficient the required shedding of blood for the atonement of the people's sins. The Holy of Holies that contained the Shechinah Glory, the visible manifestation of the presence of God, could be entered only once a year by only one man, the high priest. In order for him to enter, he had to have the blood of the Yom Kippur sacrifice with him, and this blood had to be sprinkled on the Ark of the Covenant, which contained the tablets of the Law itself.

This is detailed in Leviticus 16:15-17: Then shall he kill the goat of the sin-offering, that is for the people, and bring his blood within the veil, and do with his blood as he did with the blood of the bullock, and sprinkle it upon the mercy-seat, and before the mercy-seat: and he shall make atonement for the holy place, because of the uncleannesses of the children of Israel, and because of their transgressions, even all their sins: and so shall he do for the tent of meeting, that dwells with them in the midst of their uncleannesses. And there shall be no man in the tent of meeting when he goes in to make atonement in the holy place, until he come out, and have made atonement for himself, and for his household, and for all the assembly of Israel. And so the principle stood throughout the remainder of Old Testament history . But it was a burden to the individual. These blood-sacrifices had to be repeated year in and year out and they had to be done in the Temple at Jerusalem. For the Jews living elsewhere in the country , miles from Jerusalem, it was a burden to come every year to offer their sacrifices to the Lord for the atonement of their sins. Only the faithful few , those whom the prophets referred to as the Remnant, loved God and His Law enough to do so in spite of the burden it created.

Others built their own altars on mountains and hills closer to home and offered their sacrifices there. But no atonement was granted at these rival altars, and the prophets of God railed against these practices and condemned this deviation from the Law of God. Many had failed to learn the lesson of Cain: that one cannot come to God for forgiveness in any way one may choose, but one must come in the way God Himself has chosen.

It was Isaiah the Prophet who first provided the hope that the day would come when the yearly burden would be lifted. In Isaiah 53, God declared that the Suffering Servant, the Messiah, would be the sacrifice for sin.

In Isaiah 53:10-11 we read: Yet it pleased Jehovah to bruise him; he has put him to grief: when you shall make his soul an offering for sin, he shall see his seed, he shall prolong his days, and the pleasure of Jehovah shall prosper in his hand. He shall see of the travail of his soul, and shall be satisfied: by the knowledge of himself shall my righteous servant justify many; and he shall bear their iniquities. The point of Isaiah 53 is basically this: the animal sacrifices under the Mosaic Law were intended to be of temporary duration, a temporary measure only. God's intent was for there to be one final blood-sacrifice and that would be the sacrifice of the Messiah Himself.

That is why Isaiah 53 uses the same type of wording, figures and emphasis found in the Book of Leviticus. For example, in verse 10b we have the expression: you shall make his soul an offering for sin.

This is a sacrificial concept; these are words that come out of the Mosaic Law itself.

And in verse 11b we read: by the knowledge of himself shall my righteous servant justify many; and he shall bear their iniquities. Not only are these words of sacrifice used generally in the Old Testament Law, but more specifically , we read of these very terms in Leviticus 16, which is the chapter that expounds and explains all the details regarding the Yom Kippur or Day of Atonement sacrifice.

This, then, was the reason why Messiah had to die: to provide the blood-sacrifice for sin once and for all. No longer would the Jews be burdened with the yearly sacrifices. All a person would need to do is accept the Messiah's death on his behalf and his sins are forgiven. Messiah had to die in order to provide that atonement, for blood is the means of redemption.

Another key issue is found in these two verses from Isaiah 53. There is a statement here that is somewhat confusing. Verse 11b reads: by the knowledge of himself shall my righteous servant justify many. A more literal translation from the Hebrew text would read like this: “the knowledge of him shall my righteous justify many.”

The word for knowledge is a Hebrew word that emphasizes experiential knowledge, not mere head knowledge. This is a knowledge of the heart or a knowledge of faith. Those who have a faith-knowledge of this Servant, by “the knowledge of him,” that He died for our sins, not by the knowledge of himself, He will, as a result, justify us. Justification means, “to be declared righteous.” We cannot be declared righteous unless our sins have been atoned for. Our sins can only be atoned for by the shedding of blood; the Messiah's blood would be the final blood that would be sacrificed.

The God of Adam and Eve is the God of Moses. It is written that God never changes so his law doesnt either. During the time of Adam and Eve God spoke directly to the human family therefore the law did not need to be written as in the days of Moses when God spoke to only a chosen few. Also, Cain and Abel would have not known the leisurely life Adam and Eve knew in the Garden since they were born after Adam and Eve got kicked out so they would have been knowledgeable in the proper offerings to God and his required law for their entire lives growing up since God spoke to them directly.

It was an offering for God to share a meal with them.

At that point, God still moved regularly among the people of the world; Cain and Able knew God personally. When God called out to Cain after Able's death, Cain wasn't surprised to be talking to God; he just retorted that keeping track of his brother wasnt his job. Later in that chapter of the book of Genesis, we learn it isn't until the time of Adam's grandchildren that any sort of formalized worship of God began.

So, what would the purpose of the meal be, if not formal worship? It's my belief that it was a meal of fellowship, shared with God. God came over to their houses one day, and they offered him dinner, just like you would offer a meal to any other friend or honored guest. The reason why God liked Abel's meal better wasn't because God preferred animal sacrifice, but because Abel put more care into it. Abel offered God a firstborn calf, the very best of his herd, while Cain just offered God an ordinary portion of his crops - quite possibly after he had already taken the best bits of his harvest for himself!

A view that I postulate is that Abel knew the prophecy in Genesis 3:15 (NIV) which says:

And I will put enmity between you and the woman, and between your offspring and hers; he will crush your head, and you will strike his heel.”

He likely had given much thought to that promise and believed that blood would have to be shed, someone would have to be ‘bruised in the heel,’ so that mankind might be uplifted again to the state of perfection that Adam and Eve had enjoyed before their rebellion. (Hebrews 11:4)

The leather coats Adam and Eve wore everyday were a constant reminder that someone/thing else had to die to cover their shameful nakedness before a holy God. An atonement (covering, reconciliation) needed to be provided. When God came looking for them, they tried to cover themselves and hide. Animal skins were God's method, God's way, because of the image of shed blood and substitution it clearly portrayed. It seems pretty obvious that more skins had to be provided when Cain and Abel came along, unless Adam and Eve let their kids run around naked as they grew into men. More death, more reminders of the price of sin and the price to make them presentable to God. Mom and Dad would have probably shared what happened as a warning to their boys - 'this is why we do this.' I'm assuming this happened. It's also important to note that Cain and Abel both knew good and evil experientially. They were born with the sin nature passed down from Adam and so they already had God's moral law (the knowledge of what was "good") written on their hearts. Romans 1:18-20 tells us that basically all men know about God's character through creation. Cain and Abel both knew what was right in God's eyes and what was wrong, as did their parents. They knew it both in theory and in practice. If you gave Abel and Cain copies of the Ten Commandments they probably would not have been surprised by any of them. Hhmmm...

As one traces the thread of animal sacrifice through the OT, from Abel to Noah just after the flood, through the life of Abraham, Isaac and Jacob, (and Job's sacrifices for his children), it becomes clear that the practice was pretty common, among the physical children of Abraham as well as among pagan idol worshippers of the times. (in fact, Heb. 11 is a great place to trace this out). By the time Moses led the Israelites out of captivity and God revealed more of his character on Mt. Sinai through the giving of a codified moral law (10 Commandments), the practice of animal sacrifice naturally became codified too, in exact detail. It was already there throughout history and so God just worked it into their official national religion.

It's important to note that the Ten Commandments and the sacrifices were not two separate concepts in the sense that God thought, "Oh no! What if they can't keep my Law?!!" and later added the sacrificial system as an afterthought. Together they were all part of God's revelation to his people. The former was an expression of God's perfect standard of morality, the latter an expression of God's grace in providing worshippers a way they could attain (through faith) a right-standing before him. If we approach Scripture by continually asking, "What does this teach me about WHO God is?" then we see that from Genesis 3 all the way to Sinai, God was revealing himself. He was saying, in effect, "I am perfectly holy and just and you can only approach me one way - through a substitutionary sacrifice." The threat he issued to Adam in Genesis 2:17 that Adam would DIE was something that God made arrangements all along to absorb in order to reconcile his children back to himself (note that God killed the first animal himself to cover Adam and Eve). The imperfect temporal picture of substitution was painted through an official codified system of continual on-going animal sacrifice. But when the fullness of time came (goosebumps), God stepped out of eternity into time to absorb the full weight of humanity's sin in HIMSELF on the cross (see Isa. 53).

The commandments and the sacrificial system were instituted together, at the same time on Mt. Sinai. The sacrificial system was the official expression of what people had already known for centuries - something/someone had to die in their place to make them presentable to God. Cain and Abel already knew this thousands of years before. One brother believed and was accepted by faith when he offered the best of his flock (Heb. 11), while the other was not willing to come by God's prescribed way (repentance, faith and blood sacrifice) and was therefore rejected by God.

Perhaps animal life sacrifice was begun by God himself in:

All Scripture is quoted from the King James translation, unless otherwise noted.

Genesis 3:21 Unto Adam also and to his wife did the LORD God make coats of skins, and clothed them.

Cain and Abel would have been familiar with this since an animal would also have to be sacrificed to make clothing for them, and at that time they were vegetarian, so there would have been no skins left from their food to make clothes for them.

There is probably no connection between Cain's giving of vegetation since he was the one who tilled, while Abel was the tender of the flock. Each was giving the fruits of their labor.

Since both were old enough to labor it is probable that many animals had been sacrificed to provide clothing for the whole family, and so animal sacrifice would already be somewhat justified in protecting them from the elements, and to hide their nakedness.

Also although it is not mentioned prior to this it is most likely that Adam and Eve had produced daughters by this time.

Genesis 5:3 through 5 And Adam lived an hundred and thirty years, and begat a son in his own likeness, after his image; and called his name Seth: 4 And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters: 5 And all the days that Adam lived were nine hundred and thirty years: and he died.

A little math tells that the death of Abel took place sometime between Adam's creation and 130 years when Seth was born.

Hope this helps.

Though many interpret God's rejection of Cain's sacrifice to be because it was not a blood sacrifice, the text doesn't support it. One has to take from another context and make suppositions to arrive at that conclusion. I believe the text tells explicitly the reason for the rejection.

But first, let's look at sacrifice. Sacrifice was not used only for atonement, but for thanksgiving and communion with God as well. Also, there is no indication in the text that the two were approaching God for forgiveness, so the sacrifices could be an offering of thanksgiving and praise. Or a seasonal celebration of the yields of each man's work rendered to the Lord to sanctify the rest of the crop and/or flock. Sacrifice is not about giving something up, but about making things holy, or acceptable to God, that were either not holy before or were needed for restoration to acceptability after a breach (for sin).

The first blood spilled was not that of an animal but Adam's when God took Eve from his being. So that was a sacrifice that brought about wholeness for Adam, though something was taken from him. He gained wholeness in having a companion of like nature to share and produce forward in life, for God had said, "It is not good that Adam be alone." Therefore, the first sacrifice was initiated by God for human wholeness.

In the text of Cain and Abel, God tells Cain the reason he rejected the sacrifice--because he had done it in the wrong spirit: "if you do well, you will be accepted." This is a theme that runs through several of the prophets in decrying the people's presumption that God would accept their sacrifice (not only for sin, but also for praise, thanksgiving, and communion) regardless of their attitudes and mistreatment of the fellow human beings. God is pointing to Cain's growing root of bitterness and telling him to repent of that first, then offer sacrifice.