A Theory on the powers of the innocent first parents...

Theory:
That Adam and Eve were not created with the power to choose between good and evil, but were granted this power subsequently, and that this power is not, therefore, part of our nature, but something added.  (Therefore, the resolution of this power, or its removal entirely, is not a violation of our nature.)

Such a choice has as prerequisite the knowledge of the two, and since they were created innocent -- without that knowledge -- they did not therefore have the power to choose between them.
-------
Option A:
They were not even created with the power to choose the knowledge.  This was a gift of God, and the beginning of His tutelage of them as children, with an eye toward bringing them to full sonship.  He planted the garden, and placed them in it, and only then did He cause the trees to grow, including "the tree of life also in the midst of the garden, and the tree of knowledge of good and evil".  And only then did He give the commandment, thus giving them, by the commandment, the power to obey or disobey, and by the tree, the potential to obtain the knowledge of good and evil.

Option B:
They were, however, created free -- that is, with the power to disobey (or, more significantly, with the power to seek the source of their life and knowledge from else but God Himself), and they could not know, of course, that this was not good, since they had not the knowledge of good and evil.
--------

"Thou shalt surely die", rather than being a threat, constituted the warning label on the package.  Not a Divine Decree of Punishment, but a Divine Warning of Consequences, for the Deity has the knowledge of good and evil in Himself, and therefore knows very well it's contents.  To see that this is so, one needs merely to remember that He created all things.  As such, He Himself is the provider of the nature of all things, including the Tree of the Knowledge of Good and Evil, and therefore, He must have the Knowledge of Good and Evil in Himself, or there could have been no Tree.

And He knew (as we now know) that the knowledge of good and evil is obtained only in death, and so to partake of the fruit of that tree is to die.  Thus the warning.

Knowledge of something, in the Biblical sense, is the experience of that thing, and not so much merely cognizance of information in the abstract.  Both good and evil can only be known by experience, then, and the experience of both, I will show briefly, includes undergoing death.

With respect to the Good -- Good is God, and God is Love.  Ergo, to Love is to know Good, and the only true Good is to Love as greatly as possible (anything else, while good, is not the fulness of goodness, and so cannot be considered truly to be the "knowledge of good").  The greatest Love possible is for a man to lay down his life for his friend.  Ergo, the complete knowledge of Good is only obtained through the experience of death.  QED

With respect to Evil -- God is Good, and the giver of Life.  Ergo, Evil is the separation from God, and from Life, and this, of course, is death.  Therefore, the knowledge of evil is obtained by the experience of death as well.  QED.

This is why there is one tree, of the knowledge of both good and evil, and not two trees, one of the knowledge of good and the other of the knowledge of evil.  The two are obtained by the same means, and so the one tree is the tree of Death, the experience is the knowledge of both.

This is also why there is no greater Love than to undergo death on behalf of the beloved.  Because death itself is evil, to allow yourself to be slighted, to be evilled -- to coin a term -- in order to give the other life -- this is the nature of God, of grace, of mercy.

But I digress.

In time, God would have prepared the Man to receive this knowledge -- this experience of Death -- with faith in Himself and His power to Resurrect, to overcome Death -- Faith that the Darkness does not overcome the Light, but is swallowed up by it.  They would have eaten, at His command, with faith and love, knowing that in eating they would die, but believing that He would raise them up again -- which He would have done -- and they would then have eaten of the Tree of Life, and lived forever as Sons of God with the knowledge of good and evil, and with eternal life.  This has, I think, always been His plan.  Their disobedience was not a "derailment" of His plan from which He then had to recover, but rather an exercise of the freedom He gave them with the grace of the commandment.   It had the same result, in the end, because even when we are faithless, He remains faithful -- He cannot deny Himself.

Instead, they considered equality with God a thing to be grasped, rather than received, and, stretching forth their hands to the tree, partook of Death.

But the callings and purposes of God are without repentance; they are only delayed or hastened by the choices of the Man.

Since they partook without the fear of God, without faith, they (and their descendents) were deprived of the grace that comes through faith and drives away all fear.  They discarded the commandment, and so the grace of the commandment was discarded with it.

Therefore, they were not only subject to death itself, but to the Fear of Death, by which they were thenceforth held under bondage to sin, and although they now had open eyes, and knew good and evil, they had now lost their former power to obey.  (There being no commandment remaining to obey.)

Nevertheless, the goodness of God began immediately to prevail -- He remaining faithful, as noted above.  He commenced posthaste the long and arduous process of cleansing them and restorin them to their former state.  And, since they had jumped ahead, He Himself in His mercy jumped further ahead -- as is His wont -- took the evil done and turned it into good, not only undoing all the damage, but furthermore bringing them to glory.  Not only restoring their innocence, but giving them power to become the Sons of God, as was the plan in the first place.  Not only clothing them with skins, but with Himself.  Not only binding death, but destroying it.

But I get ahead of myself.

Having seen that the Man had gotten ahead of Himself, and thereby lost His power to not only desire, but to choose the Good, He immediately acted to restore that power to some degree (although not thoroughly, since, regardless of their ambition, they were not as yet quite mature, and in addition to needing to learn faith, also now needed to learn patience), by giving them an example, and a commandment to follow it.  (Since it is His Word that, being Good, enables goodness at all, which they had, as we noted early, recently discarded.)

Grace comes through faith(fulness).  Having been unfaithful, they had fallen from the grace given to them.  Now He restored to them some measure of grace by providing another commandment -- another means of faithfulness.  This He provided as a gift, in His mercy, and so even then, in that primitive time, they had no room to boast, even if they remained faithful from thenceforth, seeing as they received the commandment with its opportunity the same way as in the beginning -- not as deserved, but as a free gift, prevenient, and not merited.  (This is, of course, God's nature: He sends His rain on the just and the unjust.)

And so, by degrees of faithfulness and faithlessness, this dance played out, each round amplified and more detailed, but following the same pattern (for both natures remained the same), until finally the time was come to full term, and God Himself not only restored the example and commandment, but Himself became both the Man and the example, and fulfilled all commandment in Himself, remaining Faithful.  He, as the Man Himself, in due time, underwent Death by obedience, and stretched forth His pure hands upon the Tree, not grasping for divinity, but in faithfulness and with faith, for His Love of the Beloved, giving His Life for (and to, by the Spirit of God) His Friends.

Therefore He, as the Man, was exalted to the Right Hand of God by God, as was planned from the beginning for the Man, and thereby communicated from the Father to all mankind in Himself the Holy Spirit, the Giver of Life, and restoring once and for all in Himself the ancient power, sanctifying and glorifying those who die with and in Him to be the sons of God, who cry "Abba, Father" in their hearts with Him.

Thus the Commandment has gone forth yet again, and finally -- the grace of God enabling faith and faithfulness by it, and calling all to the same.

"The Law shall go forth from Zion, and His Word from Jerusalem."

"The LORD hath made bare His holy arm in the eyes of all the nation; and all the ends of the earth shall see the salvation of our God."

"The whole earth is full of His glory!"

"For if we be dead with Him, we shall also live with Him.
If we suffer, we shall also reign with Him.
If we deny Him, he also will deny us.
If we are faithless, yet He abideth faithful: He cannot deny Himself."