How Man is the Image of God. Whether the Woman is Not Also the Image of God. How the Saying of the Apostle, that the Man is the Image of God, But the Woman is the Glory of the Man, is to Be Understood Figuratively and Mystically
12 For, as not only most true reason but also the authority of the apostle himself declares, man was not made in the image of God according to the shape of his body, but according to his rational mind. For the thought is a debased and empty one, which holds God to be circumscribed and limited by the lineaments of bodily members. But further, does not the same blessed apostle say, “Be renewed in the spirit of your mind, and put on the new man, which is created after God;” and in another place more clearly, “Putting off the old man,” he says, “with his deeds; put on the new man, which is renewed to the knowledge of God after the image of Him that created him?” If, then, we are renewed in the spirit of our mind, and he is the new man who is renewed to the knowledge of God after the image of Him that created him; no one can doubt, that man was made after the image of Him that created him, not according to the body, nor indiscriminately according to any part of the mind, but according to the rational mind, wherein the knowledge of God can exist.
And it is according to this renewal, also, that we are made sons of God by the baptism of Christ; and putting on the new man, certainly put on Christ through faith. Who is there, then, who will hold women to be alien from this fellowship, whereas they are fellow-heirs of grace with us; and whereas in another place the same apostle says, “For you are all the children of God by faith in Christ Jesus; for as many as have been baptized into Christ have put on Christ: there is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female; for you are all one in Christ Jesus?” Pray, have faithful women then lost their bodily sex?
But because they are there renewed after the image of God, where there is no sex; man is there made after the image of God, where there is no sex, that is, in the spirit of his mind. Why, then, is the man on that account not bound to cover his head, because he is the image and glory of God, while the woman is bound to do so, because she is the glory of the man; as though the woman were not renewed in the spirit of her mind, which spirit is renewed to the knowledge of God after the image of Him who created him?
But because she differs from the man in bodily sex, it was possible rightly to represent under her bodily covering that part of the reason which is diverted to the government of temporal things; so that the image of God may remain on that side of the mind of man on which it cleaves to the beholding or the consulting of the eternal reasons of things; and this, it is clear, not men only, but also women have.
Source: On the Holy Trinity (New Advent)