The womb of Mary was, therefore, to our Redeemer a voluntary prison, because it was a prison of love. But it was also not an unjust prison: he was indeed innocent himself, but he had offered himself to pay our debts and to satisfy for our crimes. It was therefore only reasonable for the divine justice to keep him thus imprisoned, and so begin to exact from him the due satisfaction.
--St. Alphonsus Liguori, The Incarnation, Birth and Infancy of Jesus Christ
