Read what you post.
"For if we, being enemies, were reconciled to God through the death of His Son,
much more we will be saved in His life,
having been reconciled"
And once again you are but quotemining. Romans is one letter. For convenience and aesthetics, it is broken up into 16 Chapters, but it is still all one letter. In it Paul returns again and again to the message that it is behavior that is important.
Christianity is a message of life, of love. You keep trying to drag us off into totally unrelated issues. The question was, "Why was Cain's sacrifice unacceptable?"
The answer is, No one knows. But it has NOTHING to do with Jesus, nothing to do with the crucifixion, nothing to do with the resurrection. All of these are but dancing goal posts you bring in when you don't like the answers given.
You seem fixated on Jesus crucifixion. But if Jesus came down and became man, he was going to die. If GOD wanted to forgive sins, becoming man and killing himself and arising from the dead is just plain stupid. GOD could forgive mankind simply by forgiving mankind. GOD does not have to sacrifice himself to himself to do that.
GOD became man as a message. He became one of us, lived and died as one of us, taught us how we should live, showed us that life everlasting is a reality, told us what we needed to do.
Love GOD and love others as we love ourselves.
It really is as simple as that.
Aslan is not a Tame Lion