Letters of St. Macarius of Optina.
I repeat you about the prayer that the very thought to have the action of grace from the warmth is already delusion: the kingdom of God cometh not with observation (Luke 17, 20). Prepare your heart by fullfillment of the commandments of God, cleansing it from passions, and descend into the deepest humility, learning and seeing your weakness; and when you have the guarantee of humility in your heart, it will be already safe from the delusion of the enemy and the grace of God itself will write its own laws in it. The Saints, who had grace in themselves, considered themselves as not having reached it, and this very humility kept them safe; and who thought to have grace was driven by pride and was deluded…