Wherefore Our Savior said in the Gospel: ‘That which is born of the flesh is flesh, and that which is born of the Spirit is spirit.’ 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.
-St. John of the Cross