The perpetual virginity of Mary “matters” because it was fitting and proper, and preserved the miracle of the virgin birth and the uniqueness of the incarnate God. If she had had other children, then that miracle would be doubted. And would anyone really want a brother Who was God? Talk about sibling conflicts and an inferiority complex!
We’re not required by the Church to intuitively “feel” this doctrine, but we have to accept it as a de fide dogma of the Catholic Church (that is, a doctrine possessing the very highest authority and certainty of truthfulness). If it weren’t important or necessary, it wouldn’t have been declared to be so.
We don’t have to “resonate” with every doctrine or fully understand a doctrine in order to accept it in faith, by the authority of the Holy Catholic Church. If God (through the Church) had decided that perpetual virginity wasn’t necessary, then I would accept that as God’s will and defend that.
God could have become man (or not become man) and saved humanity any way He wanted to. It was not intrinsically necessary for there to be a virgin birth, or even for Jesus to die on the cross. God could have chosen to save us in another fashion. He’s God. He can do as He pleases. But as it is, He decided that Mary’s perpetual virginity was fitting and proper, and to come and suffer and die on the cross on our behalf, out of His amazing love and mercy, and we believe those are the facts of the matter, based on biblical data and universal early Christian tradition.
It’s often stated tat this doctrine presupposes that sex is evil or that even married sex is evil or if not evil, somehow unholy or something to be ashamed of: as if the Church teaches that it is a bad thing. The Church is not “anti-sex” because it extolls consecrated virginity. Marriage is a sacrament (meaning that it gives grace to the married couple).
It’s true that we think the evangelical counsels, or voluntary service of the priest or nun is a higher calling, because it is an undistracted devotion to the Lord: as St. Paul says. It’s heroic renunciation for the kingdom’s sake. But we don’t regard marriage or married, moral sex as “bad” because of that.
It’s a case of “very good” or “excellent” (marriage) and “best” (consecrated virginity). Protestant polemics in the 16th century created the false dichotomy and attributed it to Catholic teaching because they had ceased teaching that a consecrated celibate state was biblical and helpful to the Church.
But it is quite explicitly biblical indeed. St. Paul devotes an entire chapter to it (1 Corinthians 7). So it’s another case where Catholics are much more biblical than Protestants: who always regard themselves as “the Bible people.”
Photo credit: Lower portion of The Annunciation (c. 1436), by Jan van Eyck (c. 1390-1441) [public domain / Wikimedia Commons]