Why did the blood sacrifice in Genesis take place as acceptable to God? I have asked pastors where is it commanded by God to have a blood sacrifice as an offering in Genesis since that is the beginning.  It doesn't seem to be explained until Leviticus.  Can someone please tell me if God commanded this to be done in Genesis? Where in Genesis was it commanded that sacrifice was necessary.  From what I am reading it appears to be open as an interpretation.
In the Pearl of Great Price in the book of Moses it says:(Moses 5:5-7)


  5 And he gave unto them commandments, that they should worship the
  Lord their God, and should offer the firstlings of their flocks, for
  an offering unto the Lord. And Adam was obedient unto the commandments
  of the Lord.
  
  6 And after many days an angel of the Lord appeared unto Adam,
  saying: Why dost thou offer sacrifices unto the Lord? And Adam said
  unto him: I know not, save the Lord commanded me.
  
  7 And then the angel spake, saying: This thing is a similitude of the
  sacrifice of the Only Begotten of the Father, which is full of grace
  and truth.


When Adam left the Garden of Eden he was commanded by God to give a sacrifice. We see this is continued on by his sons with the whole Cain and Abel situation. It was meant as a similitude of Christs sacrifice. So when Christ died on the cross that law was fulfilled and it was no longer needed for man to sacrifice living animals though Christ has asked other sacrifices of man.

I don't think there is anything written in Genesis specifically if you look at it chronologically but if you look at the story of Abraham and his son Isaac Genesis talks about sacrifice there. But it doesn't explain anything or imply whether sacrifice had been happening before. It is an interesting story as Abraham was almost sacrificed by his own father and that was the reason he left his homeland, so for him to do the same to his only son was very significant.

It was probably written in other scriptures that have not survived to this time era, which is unfortunate as that would have been interesting.