Why was it necessary for Mary to be married?

What Paul calls the foolishness of the gospel starts not with Mary’s “Let it be…” to the angel but with her “I do” to Joseph.

Believers often speculate about the nature of Mary’s relationship with Joseph after she gives birth to Jesus. If the Lord Jesus is “born of the Virgin Mary,” as the creeds attest, then does the God-bearer remain a virgin thereafter? Does the Son condescend into a normal family; that is, do his parents subsequently enjoy a normal sex life?

Though the scriptures are inconclusively quiet on the question, the tradition has nevertheless ventured answers. The church asserted the perpetual virginity of Mary, for instance, at Fifth Ecumenical Council in Constantinople in 553 A.D., a doctrine that unites the church, east and west. Indeed in the early third century, Origen considered Mary’s perpetual virginity a settled item of dogma. The modern Catholic belief that Mary was conceived apart from sin— and so born free from it— makes the question even more of a muddle. As St. Augustine notes in City of God, it’s quite impossible for sinners such ourselves even to conceive what sexual intimacy, freed from the effects of the fall, will be like for us in the Fulfillment. Even if the scriptures provided an answer on the question, we nonetheless could not comprehend it in the affirmative.

As much as the nature of the Holy Family’s marriage elicits curiosity, Origen instead pondered a detail of the Lord’s nativity which we tend to ignore altogether.

Why was it necessary for Mary to be married?