How God uses Purgatory to make the soul wholly pure. The soul acquires in Purgatory a purity so great that were it well for it still to stay there after it had been purged of sin, it would no longer suffer.
I see, too, certain rays and shafts of light which go out from that divine love towards the soul and are penetrating and strong enough to seem as though they must destroy not only the body but the soul too, were that possible. Two works are wrought by these rays, the first purification and the second destruction.
Look at gold: the more you melt it, the better it becomes; you could melt it until you had destroyed in it every imperfection. Thus does fire work on material things. The soul cannot be destroyed in so far as it is in God, but in so far as it is in itself it can be destroyed; the more it is purified, the more is self destroyed within it, until at last it is pure in God.
When gold has been purified up to twenty-four carats, it can no longer be consumed by any fire; not gold itself but only dross can be burnt away. Thus the divine fire works in the soul: God holds the soul in the fire until its every imperfection is burnt away and it is brought to perfection, as it were to the purity of twenty-four carats, each soul however according to its own degree. When the soul has been purified it stays wholly in God, having nothing of self in it; its being is in God who has led this cleansed soul to Himself; it can suffer no more for nothing is left in it to be burnt away; were it held in the fire when it has thus been cleansed, it would feel no pain. Rather the fire of divine love would be to it like eternal life and in no way contrary to it.