XVI. A contemplation of the Divine utterance which said— Let us make man after our image and likeness ; wherein is examined what is the definition of the image, and how the passible and mortal is like to the Blessed and Impassible, and how in the image there are male and female, seeing these are not in the prototype .
12 Now as the image bears in all points the semblance of the archetypal excellence, if it had not a difference in some respect, being absolutely without divergence it would no longer be a likeness, but will in that case manifestly be absolutely identical with the Prototype. What difference then do we discern between the Divine and that which has been made like to the Divine? We find it in the fact that the former is uncreate, while the latter has its being from creation: and this distinction of property brings with it a train of other properties; for it is very certainly acknowledged that the uncreated nature is also immutable, and always remains the same, while the created nature cannot exist without change; for its very passage from nonexistence to existence is a certain motion and change of the non-existent transmuted by the Divine purpose into being.
13. As the Gospel calls the stamp upon the coin “the image of Cæsar,” whereby we learn that in that which was fashioned to resemble Cæsar there was resemblance as to outward look, but difference as to material, so also in the present saying, when we consider the attributes contemplated both in the Divine and human nature, in which the likeness consists, to be in the place of the features, we find in what underlies them the difference which we behold in the uncreated and in the created nature.
14. Now as the former always remains the same, while that which came into being by creation had the beginning of its existence from change, and has a kindred connection with the like mutation, for this reason He Who, as the prophetical writing says, “knows all things before they be,” following out, or rather perceiving beforehand by His power of foreknowledge what, in a state of independence and freedom, is the tendency of the motion of man's will,— as He saw, I say, what would be, He devised for His image the distinction of male and female, which has no reference to the Divine Archetype, but, as we have said, is an approximation to the less rational nature.
15. The cause, indeed, of this device, only those can know who were eye-witnesses of the truth and ministers of the Word; but we, imagining the truth, as far as we can, by means of conjectures and similitudes, do not set forth that which occurs to our mind authoritatively, but will place it in the form of a theoretical speculation before our kindly hearers.
16. What is it then which we understand concerning these matters? In saying that “God created man” the text indicates, by the indefinite character of the term, all mankind; for was not Adam here named together with the creation, as the history tells us in what follows? Yet the name given to the man created is not the particular, but the general name: thus we are led by the employment of the general name of our nature to some such view as this— that in the Divine foreknowledge and power all humanity is included in the first creation; for it is fitting for God not to regard any of the things made by Him as indeterminate, but that each existing thing should have some limit and measure prescribed by the wisdom of its Maker.
17. Now just as any particular man is limited by his bodily dimensions, and the peculiar size which is conjoined with the superficies of his body is the measure of his separate existence, so I think that the entire plenitude of humanity was included by the God of all, by His power of foreknowledge, as it were in one body, and that this is what the text teaches us which says, “God created man, in the image of God created He him.” For the image is not in part of our nature, nor is the grace in any one of the things found in that nature, but this power extends equally to all the race: and a sign of this is that mind is implanted alike in all: for all have the power of understanding and deliberating, and of all else whereby the Divine nature finds its image in that which was made according to it: the man that was manifested at the first creation of the world, and he that shall be after the consummation of all, are alike: they equally bear in themselves the Divine image.
18. For this reason the whole race was spoken of as one man, namely, that to God's power nothing is either past or future, but even that which we expect is comprehended, equally with what is at present existing, by the all-sustaining energy. Our whole nature, then, extending from the first to the last, is, so to say, one image of Him Who is; but the distinction of kind in male and female was added to His work last, as I suppose, for the reason which follows.
Source: On the Making of Man (New Advent)