On the Virginal Conception, and On Original Sin: Chapter 12/Chapter 13
ON THE VIRGINAL CONCEPTION, AND ON ORIGINAL SIN
and Eve, who is from a man alone, are all just as much genuine human beings as is any man or woman who is from both a man and a woman. Now every human being is either Adam or from Adam, but Eve is from Adam alone, and all others are from Adam and Eve. For since Mary, from whom alone Jesus came, is from Adam and Eve, Jesus cannot but be from both Adam and Eve.
And it was fitting that in this way the one who was to redeem the human race should be, and be born from, the father and mother of all.
Chapter 12 That it would not be right for Adam's evils to be transmitted to that man
And the following considerations likewise make it easy to understand how the son of the Virgin was not subject to the sin or debt of Adam.Adam was created just, free from sin and its much-discussed debt and from punishment for sin, happy, and capable of always preserving the justice that he had received and thereby also preserving the freedom and happiness of which I have spoken. Therefore, since he did not preserve for himself these good things, even though he could have preserved them for ever without any difficulty, he robbed himself of them and subjected himself to their opposites. And so he was made a slave to sin or injustice, and to a debt that he could not repay, and to that unhappiness that consists in his powerlessness to recover the good things that he had lost. It was only by failing to preserve those good things, even though he had the power to preserve them for himself, that he was able to rob himself of the good things he had possessed and attract evils that he had not possessed; accordingly, he was not able to rob others of those good things or inflict evil things upon them unless he had the power to preserve those things for them but failed to do so. Now it was only for those whose propagation had been made subject to his will that he was able to preserve these good things; therefore, he was not able to transmit the aforementioned evils to any person whose generation was not, and could not be, in any way accomplished either by the reproductive nature bestowed on him or by his will— even if that person were propagated from him. Therefore, there was no basis, and it would not have been right,for Adam's evils to be transmitted to the man who was conceived by the Virgin.
Chapter 13 That even if he were not God but merely a human being, it would still have been necessary for him to be such as the first human being was created
Furthermore, if by the pure sight of reason we gaze attentively upon God's wise justice, we will understand that it would be altogether absurd for any necessity deriving from someone else's sin or debt or punishment to be transmitted