Prayer is a prevailing course with God.
It prevails for the removing of ill, or for the preventing of ill, or for the obtaining of good, ‘I shall be delivered,’ I shall be continued in the state of deliverance; but yet you must pray. Your prayers will obtain and beg this of God.
Reason 1. Prayer is a prevailing course, because, as I said, it is obedience to God’s order. He bids us call upon him, and he will hear us. Prayer binds him with his own promise. Lord, thou canst not deny thyself, thou canst not deny thy promise, thou hast promised to be near all those that call upon thee in truth; and though with much weakness, yet we call upon thee in truth; therefore we cannot but be persuaded of thy goodness that thou wilt be near us. So it is a prevailing course, because it is obedience to God’s order.
Reason 2. And it is a prevailing course, because likewise it sets God on work. Faith, that is in the heart, and that sets prayer on work, for prayer is nothing but the voice of faith, the flame of faith. The fire is in the heart and spirit, but the voice, the flame, the expression of faith, is prayer. Faith in the heart sets prayer on work. What doth prayer? That goes into heaven, it pierceth heaven, and that sets God on work; because it brings him his promise, it brings him his nature. Thy nature is to be Jehovah, good and gracious, and merciful to thine! thy promise is answerable to thy nature, and thou hast made rich and precious promises. As faith sets prayer on work, so prayer sets God on work; and when God is set on work by prayer (as prayer must needs bind him, bringing himself to himself, bringing his word to him; every man is as his word, and his word is as himself), God being set on work, he sets all on work. He sets heaven and earth on work, when he is set on work by prayer. Therefore it is a prevailing course. He sets all his attributes on work for the deliverance and rescue of his church from danger, and for the doing of any good. He sets his mercy and goodness on work, and his love, and whatsoever is in him. – Richard Sibbes, An Exposition of 2 Corinthians 1