You appear to think that Adam would have died anyway and not on account of sin, the Fall, so that the only death he died was a "spiritual" death.
Well, why did God say to Adam regarding the tree of knowledge of good and evil "for in the day that you eat from it you will surely die." I have looked up the Hebrew word used for die in that verse in my concordance and no where else is it used in the context of spiritual death. There is no indication that die means to start the process of dying. It means exactly what it says - Adam would physically die. And yet Adam and Eve ate of it and they did not die, not for hundreds of years later.
In fact, when God finds out what happened he says "Behold, the man has become like one of us, knowing good and evil; and now, he might stretch out his hand and take also from the tree of life, and eat, and live forever." He even had to assign cherubim with a flaming sword to guard the way to the tree of life to keep man from it. Why was he worried that man might live forever when he had sworn that eating the fruit would result in death.
Also, why did God make all the plants for food? Why would an eternal being that could not die need to eat? You do realize why we eat right? We need to take in energy from the environment to maintain our body systems. Without that intake of energy, we would die. And yet if before the fall there was no death, why would Adam need to eat? Did Adam need to eat or did God make food available just for fun?
Oh, and you do realize that plants die when you eat them, right? So there WAS death. But you probably want to restrict the meaning of death to only things that breath air; oh wait ... plants breath air too. So was there ANY organisms that died before the fall? How about bacteria? Nematodes?
instead thinking that death is just a part of life and not something that entered that corrupted the life God gave, I'd think it would make Jesus' death for us hard to explain.
I don't see that. Why does it make Jesus' death hard to explain? His death would still pay the price that could reconcile us to God. Why does death being a part of the physical world change that?
The whole "no death before the fall" bit just doesn't make sense and it doesn't even fit with the Biblical evidence.
HBD
Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for... I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca
"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.
Ignorance is a most formidable opponent rivaled only by arrogance; but when the two join forces, one is all but invincible.