But as he asserts that “the Mosaic narrative most impiously represents God as in a state of weakness from the very commencement (of things), and as unable to gain over (to obedience) even one single man whom He Himself had formed,” we say in answer that the objection is much the same as if one were to find fault with the existence of evil, which God has not been able to prevent even in the case of a single individual, so that one man might be found from the very beginning of things who was born into the world untainted by sin.
For as those whose business it is to defend the doctrine of providence do so by means of arguments which are not to be despised, so also the subjects of Adam and his son will be philosophically dealt with by those who are aware that in the Hebrew language Adam signifies man; and that in those parts of the narrative which appear to refer to Adam as an individual, Moses is discoursing upon the nature of man in general. For “in Adam” (as the Scripture says) “all die,” and were condemned in the likeness of Adam's transgression, the word of God asserting this not so much of one particular individual as of the whole human race.
For in the connected series of statements which appears to apply as to one particular individual, the curse pronounced upon Adam is regarded as common to all (the members of the race), and what was spoken with reference to the woman is spoken of every woman without exception. And the expulsion of the man and woman from paradise, and their being clothed with tunics of skins (which God, because of the transgression of men, made for those who had sinned), contain a certain secret and mystical doctrine (far transcending that of Plato) of the souls losing its wings, and being borne downwards to earth, until it can lay hold of some stable resting-place.
Source: Against Celsus (New Advent)