“[I]t is wrong to think of conversion as the decision of a man or as an agreement or contract between a man and God in which grace comes to a man only as a result of his decision to allow it. For one thing such an idea suggests that men before they are converted occupy a position of neutrality or of balance or equilibrium, and that a man by his decision is able to tip the balance one way or the other, to allow grace or to resist it. But any conscious decision, any turning to God, comes about as a result of being turned by God, by being regenerated.”