It is necessary to the trustworthiness of the Gospel records. If the Gospels are wrong about the birth of Christ, they might be wrong about other details about Christ.
It is necessary to the Lord’s sinlessness. The sinful nature is passed from Adam through the human race by inheritance through conception. If Jesus had been born through a normal human union, he himself would have inherited original sin and would have himself needed a savior. Certainly he could never have been the savior of the world.
It is necessary to preserve his singular personality. Jesus was a person from all eternity. The union of man and woman creates a person. If Jesus had been born by natural procreation, he would have been some schizophrenic monstrosity. Only by bypassing the normal procreation process through the virgin birth could Jesus avoid this problem.
Stand Firm! 