The Necessity of the Incarnation

Is the Doctrine of the Virgin Birth is necessary for salvation? Al Mohler details how many "liberal scholars like Hans Kung" and "John Shelby Spong argue...that belief in the Virgin Birth is unnecessary." But what are the implications of such a belief, and on what authority do they support their claims?

If Mary was not a virgin, then Christ had a human father.

If Christ had a human father, then He was not God.

If Christ was not God, then He was not a sufficient sacrifice for sins.

If Christ was not a sufficient sacrifice for sins, then we are all hopelessly lost.

Thus the Doctrine of the Virgin Birth is necessary for salvation.