If the virgin birth of Jesus is untrue, then the story of Jesus changes greatly; we would have a sexually promiscuous young woman lying about God’s miraculous hand in the birth of her son, raising that son to declare he was God, and then joining his religion. But if Mary is nothing more than a sinful con artist then neither she nor her son Jesus should be trusted. Because both the clear teachings of Scripture about the beginning of Jesus’ earthly life and the character of his mother are at stake, we must contend for the virgin birth of Jesus Christ
John Piper
From the book “Supremacy of Christ in a postmodern world”