Why did Mary need to remain a virgin during pregnancy according to those who deny the perpetual virginity doctrine?

Question

After much editing and clarifying through comments this question seems to have asked and had answered from Catholic perspective why Mary stayed a virgin throughout her pregnancy.

Yet many Christians do not agree with perpetual virginity doctrine but still agree that Mary did remain virgin until after giving birth based on Matthew 1:25:

And knew her not till she had brought forth her firstborn son: and he called his name JESUS (KJV).

What biblical reasons are there for the necessity of Mary and Joseph to abstain from sexual relations during the time she was carrying the baby Jesus?

Answer 1

Ever-virgin dogma is the belief that Mary was a virgin during pregnancy, during birth, and after Christ's birth in her marriage to Joseph.

Whether one submits to this Papal dogma or is someone who believes that Christ was born normally or Mary/Joseph had sex and children sometime after His birth, they both, indeed all Christians, believe the prophecy that the virgin would conceive and bear a son.

Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel. Isaiah 7:14

The virgin will CONCEIVE (get pregnant) and the virgin will BEAR (bring forth, travail, deliver). Two-pronged prophecy: Conceive and give birth as a virgin.

IOW, even the same question posed for a Catholic answer was given Isaiah 7:14.

So again, the reason why Mary had to remain a virgin during her pregnancy was to fulfill scripture.

PS. This answer really has nothing to do with what came later that the Catholic dogma denies: that is, whether Mary/Joseph consummated their marriage or not (they did), whether Mary took a vow of chastity or not (she didn't), or even whether Jesus was born normally in the normal (human) way (He was). So, try not to derail the same answer that a Catholic, Orthodox, or Protestant would give.

Answer 2

The reason for no sex during Mary's pregnancy with Christ was to fulfill prophecy, to make it very clear to all.

Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel. Isa. 7:14

If Mary and Joseph had consummated their marriage prior to Christ's birth, then the prophecy fails.

As well, it would trigger the question about who the father really might have been.

Lastly, Mary and Joseph were betrothed, but not yet married at that time of annunciation. Sex would have been a sin.

Answer 3

According to Jehovah's Witnesses, Joseph and Mary may have remained abstinent until Jesus' birth in order to avoid casting doubt on who the true father of Jesus was. It also showed great respect for Mary's privilege of bearing God's Son.

The Bible says that Joseph “was righteous.” (Matthew 1:19) For example, he did not have intercourse with his virgin wife until after the birth of Jesus. This prevented any misunderstanding as to who Jesus’ real Father was. For a newly married couple to abstain from intimate relations while living under the same roof could not have been easy, but it showed that they both treasured the privilege of being chosen to raise God’s Son.—Matthew 1:24, 25.

—w02 12/15 "Lessons From the Record of Jesus' Birth"

Mary wasn't necessarily required to be a virgin according to Isaiah 7:14 since the Hebrew word used there more broadly translates to "maiden," and can refer to a virgin or a nonvirgin.

Look! The young woman [ft. note: "the maiden"] will become pregnant and will give birth to a son, and she will name him Im·manʹu·el.

Nonetheless, Matthew 1:23 is evidently a quotation of the Septuagint version of Isa. 7:14 which uses the Greek word for "virgin" in making an application of Isa. 7:14. (Insight Vol. 2 - "Virgin")

Answer 4

At some point in my studies I recall a discussion about how Mary and Joseph were spiritual persons who would have been very familiar with Jewish religious traditions and practices.

They were told that what was growing in Mary’s womb was holy. (Matthew 1:20) They would have understood that the protocols that were involved with being ceremonially clean when coming into the holy place (temple) would be fitting for one favored to carry the holiest of God’s possessions, his son, inside her body.

For this reason Mary would have felt it necessary, even mandatory, to maintain herself ritually clean to the fullest extent possible.

The Law given to Moses spelled out certain protocols that had to be followed by persons who were going to temple. Among these was the command that when a couple engaged in sexual activity, they were ceremonially unclean. They were to wash and would not be clean until the evening.

Leviticus 15:18 (NWT)

When a man lies with a woman and has an emission of semen, they should bathe in water and be unclean until the evening.

Knowing this and fully aware that for 9 months she was in effect the bearer of the holiest utensil of God’s temple, Mary would have indeed seen the necessity to refrain from sexual relations with her husband.

Expanding on this school of thought Peter Leithart wrote:

He Did Not Know Her

Joseph did not know his wife until she gave birth to a Son (Matthew 1:25). Why not?

In Matthew’s account, the conception of Jesus is attributed to the “Holy Spirit” (1:20), and Luke makes it explicit that the one conceived by the Holy Spirit is Himself holy: “the holy thing begotten shall be called the Son of God” (Luke 1:35).

Joseph might have reasoned: Since Mary was inhabited by the Spirit, and by the Holy One conceived by the Spirit, she was, or at least her womb was, holy space. If she is holy space, he cannot have sex with her, since by the rules of Torah sex defiled both the man and the woman (Leviticus 15:18). Having sex with Mary during her pregnancy would have been like a leper or a menstruant entering the temple of God. It would have been like having sex in the temple court itself.

If this is the reasoning, it sheds some light on the question of perpetual virginity. Matthew’s phrasing implies that Joseph did have sex with Mary after Jesus was born, and the reasoning above would imply the same. Temples are holy only when the Holy One inhabits them. Once Yahweh abandoned the temple, it was an empty shell for demolition and burning. If Mary was holy because the Holy One lived in her, then His birth exodus from her body would have ended her temporary holiness. She would have reverted to normal “common” status. And Joseph would have known her as his wife. Joseph refrained from sex with Mary because she was the ark, bearing the glory; but only for nine months.

This article by Leithart captures much of what I recall as to why it was necessary for Mary to remain a virgin during the entire course of her pregnancy.