Could you please expound on this? It's the first time I have ever seen the idea with regards to Adam asking God to heal Eve, and the "life for a life" comment doesn't make sense to me.
Well, it is you who first brought up the idea of Adam asking God to heal Eve. Not I. See post #(78).
My explanation of what may well have been involved is given in post #(76) and (87).
As to 'substitution' the whole idea is that the substitute is a proper substitute. Even though the animal sacrifices atoned for sin, they did not remove sin. They pointed to the true Sacrifice to come.
When any brought their animal sacrifice, a sin offering, they killed the animal and spilled it's blood. And so (Lev. 17:11) tells us that the life of the flesh is in the blood. That is the whole point of the blood. When you see the blood spilled out on the ground, the sacrifice has exchanged it's life for yours.
A life for a life. One for one.
There is no healing, no access to eternal life save through that.
The problem: How can one man die for all and God be justified in doing so.
Solution: God counts all guilty in one man. God now counts all righteous in One Man. (Federal Headship)
Understand, once sin had entered into the human race, God, because He is God, could not just overlook it. His righteousness would not allow it. He could not just look down at Adam and Eve and say "yall sure messed that up. But, I love yall so much that I'm going to let yall come into my presence anyway and live forever." He could not do it. The moment they would have entered His presence He must judge them, and kill them.
The difficulty of the salvation problem lay in God being justified in justifying you and I. I believe I mentioned (Rom. 3:26) already.
Does that help?
Quantrill