Mary's virginity is not a theological theory, it is a fact that the primitive Church was surprised to discover and transmitted with respect in its first writings, the Gospels.
Joseph is not the one who begets Jesus. Instead he is explicitly excluded: "But Mary said to the angel: 'How will this be, since I am a virgin?'" (Lk 1:34). "When he began his ministry, Jesus himself was about thirty years of age, being, as was supposed, the son of Joseph" (Lk 3:23).
"Jacob was the father of Joseph the husband of Mary, by whom Jesus was born, who is called the Messiah" (Mt 1:16). Jesus is truly begotten; the passive form manifests the transcendent character of Christ's paternal origin.
Only Mary is the human origin of Jesus; she becomes a mother while still a virgin: "Joseph, son of David, do not be afraid to take Mary as your wife; for the Child who has been conceived in her is of the Holy Spirit" (Mt 1:20)... "To fulfill what was spoken by the Lord through the prophet: 'Behold, the virgin shall be with child and shall bear a son, and they shall call his name Immanuel'" (Mt 1:22-23).
The divine origin is not attributed to the Father (masculine principle), but to the Holy Spirit (feminine in Hebrew, neuter in Greek), as seen in Matthew 1:18-20 and Luke 1:35, which excludes the mythological model of theogamy. "The angel answered and said to her, 'The Holy Spirit will come upon you, and the power of the Most High will overshadow you; and for that reason the holy Child shall be called the Son of God'" (Lk 1:35).
Mary's virginity during childbirth is evoked in John 1:13, when he speaks of Jesus, saying: "...who was born not of blood..." i.e. the blood of natural childbirth. This virginity is an echo of Jesus' life. He is the One who leaves the sealed tomb and who enters the upper room through closed doors.
Mary's virginity after childbirth is a fact that results from the converging of much of the information given in the New Testament and by the historian Eusebius of Caesarea.
By F. Breynaert