“Hear Isaiah crying out: “A child is born for us; a Son is given to us” (Is 9:6). Learn from the same prophet how the baby is born, how a son is given. Was it according to the law of nature? The prophet denies it. The Master of nature does not obey the laws of nature. But how is the child born? Tell me. The prophet answers: “Behold, the virgin shall conceive in her womb and bear a son, and they shall call his name Emmanuel” (Is 7:14), which, translated, means: God-with-us.
O marvelous event! The Virgin becomes a mother and remains a virgin! Observe this new ordering of nature. All other women, in order to remain virgins, do not become mothers; when a woman becomes a mother, she no longer has her virginity. Here, instead, the two terms are applied to the same person. For it is the same woman who is presented as mother and as virgin, for just as her virginity posed no obstacle to her giving birth, neither did her childbearing destroy her virginity. Indeed, it was fitting that (the Redeemer) having entered human life to make us all incorruptible, should Himself originate from an incorruptible birth. In fact, according to our usual way of speaking, a woman who has not had relations with a man is called “incorrupt”.”Gregory of Nyssa , On the Birth of Christ, PG 46, 1133 D-1136 B.
Gambero, L., 1999. Mary and the Fathers of the Church 1st ed. Translated by Buffer, T., San Francisco: Ignatius Press. p. 155.