Chapter 5 — Part I: The Creed — Article III: Who Was Conceived by the Holy Ghost, Born of the Virgin Mary
Section 17. Besides, what is admirable beyond the power of thoughts or words to express, He is born of His Mother without any diminution of her maternal virginity, just as He afterwards went forth from the sepulchre while it was closed and sealed, and entered the room in which His disciples were assembled, the doors being shut; or, not to depart from every-day examples, just as the rays of the sun penetrate without breaking or injuring in the least the solid substance of glass, so after a like but more exalted manner did Jesus Christ come forth from His mother's womb without injury to her maternal virginity. This immaculate and perpetual virginity forms, therefore, the just theme of our eulogy. Such was the work of the Holy Ghost, who at the Conception and birth of the Son so favoured the Virgin Mother as to impart to her fecundity while preserving inviolate her perpetual virginity.