They were also supernatural beings, endowed with "preternatural graces" beyond the capabilities flowing from their physiology [CCC #377]. These were somewhat akin to what we now think of as "paranormal powers" (telepathy etc.) They were not intrinsic to what it meant to be human. Rather, they made our first, simple, ancestors "super-human". These graces were not the same thing as "sanctifying grace" (which is friendship with God: a status or condition of being, not a power or ability). Neither did they necessarily flow from it. They were undeserved, being God's generous free gift to our first ancestors.
God set before our first ancestors a choice. He told them of the existence of the "Tree of Knowledge of Good and Evil", and warned them that if they ate its fruit they would die. It is unclear exactly what the immediate effect of eating this forbidden fruit was. Satan (the Master of Lies!) is presented as saying that it would "open the eyes" and give wisdom [Gen 3:5-5], and indeed it does seem to have had some direct effect [Gen 3:7]. Certainly, the perspective of our first ancestors on life, corporeality and each other was abruptly changed. Whether the fruit itself had an intrinsic power (as if it was infected with some virus), or whether it was rather the act of disobedience to God's injunction which had the effect of changing our ancestor's outlook on life is a moot point.
Perhaps, before "the Fall", man was a naive, simple and amoral soul; not able to conceive of ethical issues. In which case, our conscience and moral intuition comes to us as a result of eating the fruit of the "Tree of Knowledge". God first created mankind, with free-will, then let us get on with the business of developing into sentient beings with a certain independence from Him. He did this by offering the prize of "Moral Knowledge", warning what the cost would inevitably be, and standing back to let events take their inevitable, sad but necessary, desirable and eventually glorious course. This explains God's tender act of providing a first set of clothes for his wayward children [Gen 3:21].
On the other hand, this produces the difficulty that one has to conceive of our first ancestors as sub-ethical, more monkeys than men: having no sense of moral responsibility or justice beyond "obeying or not obeying", perhaps associated with fear of punishment. This is rather like the condition typical of "conservatives" or "fundamentalists" ever since! Why should God set out to deny humanity any ethical understanding? Why should its attainment have such dire consequences [Gen 3:16-19]? It would seem that before "the Fall", mankind was sub-human rather than super-human, and that the reward for moral elevation was toil, pain, suffering and death!
Perhaps God's warning that child-birth would become more painful is a clue. Objectively, giving birth is typically so painful for women because the head of a human infant is relatively huge. Perhaps, the consequence of eating the fruit of the Tree of Knowledge was a huge increase in brain-power, the gaining of "self-consciousness" and a consequential expansion of the skull! Similarly, farming [Gen 3:17-19] is a difficult affair, because of the increased demands of a knowledge and city based agricultural society, as opposed to a less civilized "hunter gatherer" existence [Gen 2:15-16].
The Fathers, following the scriptures [Wis 10:2], teach that the sin of disobedience was repented and that God forgave it; but that the consequences remained. The question then arises, "Why?" While there was no obligation on God to restore the preternatural graces, it would seem that He might have done so. They were no less deserved after the Fall than before! Much more importantly, although "sanctifying grace" was restored (without any quasi-sacramental instrumentality) its original character as "inheritable" [CCC #404] was lost. That "original justice" was inheritable and the restored "state of grace" is not was defined by the Council of Trent [Session V cannons 1&2], however no account of why is given.O God, who art the light of the minds that know thee,
the life of the souls that love thee,
the strength of the thoughts that seek thee:
help us so to know thee that we may truly love thee,
so to love thee that we may fully serve thee,
whose service is perfect freedom.Gelasian Sacramentory C5/6th
I suggest that original sin is inherited (or, if you prefer, sanctifying grace is not inherited) because the nature that we now have is different from that which characterized humanity in the beginning. Human nature was changed by the Fruit of the Tree of Knowledge. This change makes it impossible for a child to inherit the status of "Friend of God" from its natural parents, even if that child is conceived, born and brought-up by parents who are both continuously in a state of grace. Note that the idea that original sin is associated with (the pleasure associated with) sexual intercourse was condemned by Trent.
Exactly what the change in Human Nature was, I do not mean to stipulate; though I have suggested that it is self-consciousness. Unless one holds to such a position, it seems to me that it is impossible to explain why the "original justice" was inheritable, but "restored justice" not so. The original act of disobedience changed the human condition not by changing the status of Man before God (it did this, but that status was soon and easily restored - remember that Abraham and Moses were both Friends of God) but rather by changing his nature. However, it did so not by corrupting it, as Luther taught, but rather by enhancing it!
I have discussed "the guilt of original sin", and the punishment due to it elsewhere.
The icon shows the "Harrowing of Hell", with the Risen Christ trampling on the symbols of death and offering the hand of Friendship to Adam, as other Old Testament heroes and heroines stand by watching.