There is no official Church teaching that Mary's hymen remained intact (catholic.com/qa/…). Therefore, this question would probably be better phrased as, "Why do some Catholic theologians consider it important that..."

@BrianMcCutchon That's definitely not true. "Catholic" Answers isn't orthodox. The de fide dogma on her virginitas in partu (virginity during parturition) refers primarily to her bodily (physiological) virginity. How can they honestly claim "the Church has no official teaching on the physiological aspects of Jesus’ birth"?

@curiousdannii The hymen to do with virginity of the body (virginitas corporis).

@Geremia I'm not sure whether virginity counts as something physiological, but if it does, that only makes the article wrong on a technical issue of wording. Unless you consider the hymen essential to virginity, which I'm not so sure about.

@curiousdannii That's not how the Fathers considered her hymen when they likened Christ's birth to His resurrected body passing through the sealed tomb or walking through doors/walls.

@BrianMcCutchon When the Church speaks of virginity during birth, she primarily means virginity of the body.

@Geremia I agree with that, but I'm not sure whether virginity of the body requires that the hymen be intact. The Catholic Answers article quotes Fundamentals of Catholic Dogma as saying, "The dogma merely asserts the fact of the continuance of Mary’s physical virginity without determining more closely how this is to be physiologically explained." Would you agree with that statement?

@BrianMcCutchon "Would you agree with that statement?" No. The Fathers have determined "more closely how this is to be physiologically explained" by saying that it is miraculous (like how His resurrected body passed through the sealed tomb or walked through doors/walls).

@Geremia But the Fathers did not establish a dogma. To be clear, I'm not denying that Mary's hymen remained intact. I'm also not denying that the Fathers taught it. I'm just questioning whether it is dogma.

@BrianMcCutchon What does the Church mean by virginitas (corporis) in partu (virginity of the body during parturition), then?

@BrianMcCutchon That she remained a virgin during childbirth is de fide dogma.

Of course. But virginitas in partu could simply mean never having had intercourse.

That's the usual definition of virginity.

@Geremia

Though it certainly would seem fitting for Mary's hymen to remain intact, since that's at least something that's associated with virginity.

I meant correlation

@BrianMcCutchon One doesn't have intercourse during childbirth…

@Grasper That's why it's a miracle.

@BrianMcCutchon Are you arguing that her virginitas in partu isn't miraculous?