God clothed Adam and his wife with animal skin. This would have been the first sacrifice, and it was made by God because of their sin. When did man start making animal sacrifices for sin?
Genesis 3:21
ESV - 21 And the Lord God made for Adam and for his wife garments of skins and clothed them.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Why would God ever kill an animal? If he killed an animal, how did he do it? Did he simply make the animal stop breathing?
When God instituted animal sacrifice he gave the people instructions on how it would be done. He told them what to do with every part of the animal, entrails and all. All other references to animal sacrifice are assumptions. I don't believe we're left to make assumptions about such an important ordinance. But it hasn't stopped us from doing it.
I have a study Bible my dad gave me when I was new in the faith (I started doing more than just going to church, I started studying scripture) that says Cain's sacrifice needed to be a blood sacrifice "based upon previous knowledge," and it uses Gen 3:21 as a proof text. I didn’t buy it all those years ago, and I still don't.
Cain was rejected because God knew he was a murderer. It was written all over his face.
It is an assumption that he needed to bring an offering of a product from a trade of which he wasn't employed. Nothing had been said to us about blood sacrifices.
Blood sacrifice was instituted by God as worship to him down in Egypt. It is a commemoration: The Passover (Exodus 12).
Your lamb shall be without blemish, a male of the first year: ye shall take it out from the sheep... ye shall keep it up until the 14th day... the whole assembly of the congregation must kill it.
I'd like someone to show me these instructions prior to this. This was the beginning of blood sacrifice, officially.
"Your lamb shall be without blemish, a male of the first year."
Did Abraham ever hear this from God? Did Jacob or Joseph? How about Noah and his three sons? No?
But Cain and Abel did?
This is the first time Moses has ever heard of such a practice (Exodus 12). He knew the story of God appearing to Abraham. He knew the history of the Hebrew people; he had never been told anything about animals being used to signify a blood sacrifice for sin.
The institution of The Passover was the first time God spelled this out to anybody. He had not told Adam and Eve of this doctrine. Nor did he spell it out to Cain and Abel.
God is very meticulous; he doesn't show his cards;
To explain God the way many of us do, is to make him seem very unjust. It's as if Cain is given a field to work and the product of the field isn't a good enough gift for God. We're told the boys are bringing God a gift; we aren't told the gifts are for the forgiveness of their sins. But when Cain and his gift is rejected, since we now know after reading more of scripture that blood is essential for the remission of sin, and that Abel's offering of a lamb and its fat portions AND ABEL are accepted, we assume the offerings were for the remission of sin, and Cain just plain disobeyed and brought whatever he wanted to bring, after being told that his offering had to include blood being shed.
That ain't the way to study scripture; that's adding to what you think you know, and it hasn't been established.