Chapter 23
Virgin Birth

Was this doctrinal point equivalent in importance to the resurrection, or was it just a mythological claim to super-humanity? What verification do we have of its reality? None. Neither Mary nor Joseph wrote about it themselves, so we have only the word of anonymous authors as to what they said. Even if they really said it, there is no corroboration for its veracity. When we look at the Bible’s own words we find that messiahship and virgin birth are incompatible.
I guess the idea was this: to be a perfect human sacrifice, Jesus must have been perfect (without sin) when he was killed. But if Jesus was to be without sin, then he cannot have been 100% human, since humanity is tainted with original sin from Genesis. Therefore, some miracle was required.

23.1 First, would a virgin birth have been miraculous? Not necessarily. A miracle is something contrary to the known laws of nature, i.e., due to supernatural causes, especially to an act of God. But artificial insemination is not uncommon, so a virgin birth, as such, would not have needed to be a miracle.

23.2 What was the evidence for a virgin birth? None. We have only the third-hand word of an unmarried couple expecting a child.

"…an angel of the Lord appeared to [Joseph] in a dream…" Mt 1:20-25

"…God sent the angel Gabriel to Nazareth…to a virgin [Mary]" Lk 1:26-30

"How shall this be, seeing I know not a man?" Lk 1:34-35

No mention of virgin birth. Mk & Jn

Other passages left the question open of whether Mary slept with someone other than Joseph, and they didn’t say Mary was a virgin.

"…and [Joseph] knew [Mary] not till she had brought forth her firstborn son." Mt 1:24-25

"Before [Mary & Joseph] came together, she was found with child." Mt 1:18

23.3 Some parts of the Bible clearly stated that Joseph, not God, was the father.

"Is not this Jesus, the son of Joseph…" Jn 6:42

"Is not this Joseph’s son?" Lk 4:22

"His father and his mother marveled…" Lk 2:33

"His mother said…thy father and I have sought thee." Lk 2:48

"When his parents brought in the child Jesus…" Lk 2:27

"Is not this the carpenter’s son?" Mt 13:55

23.4 What prophecies necessitated a natural father to satisfy the Messiah’s Davidic descent?

"[David] knew that God had promised him on oath that he would place one of his descendants on his throne." Acts 2:30

"…I will raise up to David a righteous Branch, King who will reign wisely…This is the name by which he will be called: The Lord Our Righteousness [not called Jesus?]." Jer 23:5-6

"…I will raise up your offspring to succeed you, who will come from your own body, and I will establish his kingdom…I will be his father, and he will be my son." 2Sam 7:12-13

"…I have sworn to David my servant, I will establish your line forever…" {No mention of Jesus} Ps 89:3-4

"…One of your own descendants I will place on your throne…" {No mention of Jesus} Ps 132:11

"The Lord God will give [Mary’s son] the throne of his father David." Lk 1:32-33

23.5 How could Jesus have been miraculously conceived of God if he was a descendent of David through Joseph?

"…as to his human nature was a descendent of David." Rom 1:3

"…Jesus Christ…descended from David." 2Tim 2:8

"Theirs are the patriarchs, and from them is traced the human ancestry of Christ" Rom 9:5

"I am the Root and the Offspring of David" Rev 22:16

"From [Jesse’s] descendants God has brought to Israel the Savior Jesus…" Acts 13:23

Joseph is descended from David. Mt 1:6-16; Lk 3:23-31

"I Jesus…am the root and the offspring of David…" Rev 22:16

23.6 No prophecies necessitated a virgin birth. One prophecy was used to claim that the someone would be of virgin birth, but it obviously didn’t refer to Jesus. The prophecy applied to a sign for Ahaz, about 700 BCE, so Jesus would have been too late for this prophecy to apply to him. The passage used the word for young woman or maid (Hebrew: allmah), rather than the word for virgin (Hebrew: betula). (Gen 24:43; Ex 2:8; Prov 30:19)

"Therefore the Lord himself will give you a sign: The [young woman/maid] shall conceive [some say "is with" or "has conceived"] and will give birth to a son…" Isa 7:14

23.7 Was Mary a virgin all her life? No, she had other children.

"Isn’t this [Jesus] Mary’s son and the brother of James, Joseph, Judas and Simon? Aren’t his sisters here with us?" Mk 6:3

"…and [Mary] gave birth to her firstborn, a son." Lk 2:7

"…[Jesus] went down to Capernaum with his mother and brothers…"Jn 2:12

Other citations also.

23.8 Since other biblical births were also miraculous, why was a virgin birth for Jesus so important?

Sarah has Isaac after menopause. Gen 18:10-11

Hannah bears Samuel after her womb was closed then reopened by God. 1Sam 1:5, 2:21

Adam had no parents, but is created by God. Gen 1:27, 2:7

Eve was created from one of Adam’s ribs. Gen 3:22

Milchizedek had no mother, father, or genealogy. Heb 7:3

Immaculate Conception

23.9 Jesus can’t always have been pure according to the old Law, since he must have touched his mother during the first seven days after his birth when Mary would have been considered "unclean." In order to preserve the concept of a pure Jesus, Mary’s act needed cleaning up, so an immaculate conception was proclaimed.

"…how can he be clean that is born of a woman…" Job 25:4

"What is man, that he can be clean? Or he that is born of a woman, that he can be righteous?" Job 15:14

"…[she] who becomes pregnant and gives birth to a son will be ceremonially unclean for seven days, just as…during her monthly period…the woman must wait thirty-three days to the purified from her bleeding. She must not touch anything sacred…until the day of her purification are over." Lev 12:1

"…[impurity] will last seven days, and anyone who touches her will be unclean till evening." Lev 15:19

"When the time of their purification according to the Law of Moses had been completed, Joseph and Mary took [Jesus] to Jerusalem…" Lk 2:22

23.10 To be immaculate, Mary had to have been conceived apart from sin. How could her sinful parents have produced a pure daughter? This just adds the need for another immaculate conception on the part of Mary’s mother, Ann, and her mother, etc. That problem doesn't go away, it just keeps moving back all the way to Eve.
But was Mary really sinless according to scriptures? There is nothing saying she was sinless. The closest may be the following.

"…Mary, you have found favor with God…" Lk 1:30

If Mary was sinless, why did she need a savior? Only sinners needed a savior.

"My spirit has rejoiced in God my Savior…" Lk 1:47

But Mary cannot have been sinless according to Paul.

"All have sinned." Rom 3:23