Matthew 17:21

This kind goeth not out, &c.— Prayer and fasting could have no relation to the ejection of demons, but so far only as they had a tendency to increase the faith of miracles in him who had that power formerly conferred upon him. For example, prayer, by impressing a man's mind with a more intimate sense that all things whatsoever depend upon the infinite and incomprehensible power of God, raises his idea of that power to a greater sublimity than can be done in the way of ordinary speculation. And as for fasting, by weakening the animal life, it subdues such passions as are nourished by continual repletion of body. Hence fasting has a tendencyto free the mind from the dominion of passion, which never fails to occasion a great inward perturbation, and at times has been found to make even holy men inattentive, at least to the more silent impressions of God's Spirit. Fasting therefore produces an inward quietness and calm, very favourable to the growth of faith