The Gospels tell us that Jesus the son of Mary was born on the first Christmas Day as a result of a virginal conception nine months before. But who was responsible for such an outrageously unscientific idea? The people of that day knew as well as we do that virgins do not conceive. Was Mary raped (the Spong theory)? Was she guilty of premarital sex and lied about the Holy Spirit? Did Joseph get tricked into giving her illegitimate child the title to the royal throne of David? Or was the whole story concocted by somebody the NT critics call M (Matthew 1 & 2)? Or somebody called L (Luke 1 & 2)?
All Christians think the eternal Son of God surreptitiously slipped into our world through the womb of a woman called Mary. And most others think he had no business doing such a thing. But in any case a crime was committed. And one of the principles of detective work is that you try to think yourself into the mind of every person who might possibly be the criminal. This is exactly what the great detective Rabbi Paul recommended. Try putting yourself into the mind of the eternal Son of God. "Let the same mind be in you that was in Christ Jesus who, though he was in the form of God, emptied himself, taking the form of a slave, being born in human likeness" (Philippians 2:5-7).
Now obviously anyone who is unable to think the way God might think will be unable to locate the criminal in this case. So there is no point in discussing Paul's solution with people who refuse to adopt a Trinitarian Theistic model. You have to begin with the three persons of God united by love. You then have to picture the Son of God deciding to take birth in his own creation. He could have jumped in full grown like Shakespeare into his own play. But Paul offers a model in which the birth was by emptying from the Trinity into birth as an ordinary human, and a humble servant at that.
That means it is not so much he virgin birth that is significant but rather the virginal conception. What counts is how the Son of God came by conception into the womb of Mary. Nobody doubts that Mary provided the ovum for fertilization. What was the sperm that permitted Mary's ovum to become Jesus? Did it come from a rapist? Or from a roll in the hay with a young lover? Or from Joseph? Or from a quite unexpected source?
Paul is quite sure that any good gift, or any good fruit, or any life from the dead, or a spiritual body, can only come from the Holy Spirit. And there again if you cannot get your mind around Trinitarian Theism and the miraculous work of the Spirit, you cannot even think of what Paul has in mind. But if you do think as a Trinitarian Christian then the model that Paul uses makes it easy to imagine the sperm that penetrated Mary's ovum was energized or animated by the Holy Spirit.
We need not deny that the Holy Spirit could have worked on the sperm of a rapist, or a youthful lover, or even Joseph, to attain the divine purpose, but it seems much simpler and far more elegant to go with the virginal conception by the Spirit in Luke 1:35. I have no doubt that was Paul's explanation, and I suspect that while he was in prison in Caesarea he sent Luke to go and ask Mary, and that is exactly what she told him. But in any case as a preacher of the Good News I am committed to preaching from the canonical Gospels, and I see no reason to try and invent some other highly dubious explanation.