This passage, written by a man of deep religious experience, clearly involves and sanctions the doctrine that holy souls rest from all desires, except such as are from a divine source. There are, then, two classes of desires; — those which are the product of a fallen and unsanctified nature, and those which are from God. Agitation and sorrow always attend the one class. True peace, the peace of Christ and of angels, is the characteristic of the other.
And we proceed now to say, that the ground of difference between them is this: Desires which are from God are attended with faith; and those which are not from him are without faith. The man of the world is full of desires; but being constantly in doubt whether his desires will be accomplished or not, he is constantly the subject of agitation and grief. But the holy man, being the subject of those desires only which God has inspired within him, cannot doubt that God, who is never disappointed, will fulfill them in his own time and way. Having thus two facts in his mental experience at the same time, namely, desire and a belief in the fulfillment of desire, the element of uneasiness, which is involved in the wants of the one, is annulled by the pleasure which is involved in the supply or fullness of the other. In other words, faith stops the cravings of desire, by being itself the "substance" or fulfillment of its object; so that constant desire, supposing it to be constantly existing, is changed into constancy of fruition, constancy of peace.
— edited from A Treatise on Divine Union (1851) Part 8, Chapter 3.