7 Some of these persons make friendships of a spiritual kind with others, which oftentimes arise from luxury and not from spirituality; this may be known to be the case when the remembrance of that friendship causes not the remembrance and love of God to grow, but occasions remorse of conscience. For, when the friendship is purely spiritual, the love of God grows with it; and the more the soul remembers it, the more it remembers the love of God, and the greater the desire it has for God; so that, as the one grows, the other grows also. For the spirit of God has this property, that it increases good by adding to it more good, inasmuch as there is likeness and conformity between them. But, when this love arises from the vice of sensuality aforementioned, it produces the contrary effects; for the more the one grows, the more the other decreases, and the remembrance of it likewise. If that sensual love grows, it will at once be observed that the soul’s love of God is becoming colder, and that it is forgetting Him as it remembers that love; there comes to it, too, a certain remorse of conscience. And, on the other hand, if the love of God grows in the soul, that other love becomes cold and is forgotten; for, as the two are contrary to one another, not only does the one not aid the other, but the one which predominates quenches and confounds the other, and becomes strengthened in itself, as the philosophers say. Wherefore Our Saviour said in the Gospel: ‘That which is born of the flesh is flesh, and that which is born of the Spirit is spirit.’3838St. John iii, 6. That is to say, the love which is born of sensuality ends in sensuality, and that which is of the spirit ends in the spirit of God and causes it to grow. This is the difference that exists between these two kinds of love, whereby we may know them.
8. When the soul enters the dark night, it brings these kinds of love under control. It strengthens and purifies the one, namely that which is according to God; and the other it removes and brings to an end; and in the beginning it causes both to be lost sight of, as we shall say hereafter.
Source: Dark Night of the Soul (CCEL)