The Screwtape Letters - C.S. Lewis

"If this fails, you must fall back on a subtler misdirection of his intention. Whenever they are attending to the Enemy Himself we are defeated, but there are ways of preventing them from doing so. The simplest is to turn their gaze away from Him towards themselves. Keep them watching their own minds and trying to produce feelings there by the action of their own wills. When they meant to ask Him for charity, let them, instead, start trying to manufacture charitable feelings for themselves and not notice that this is what they are doing. When they meant to pray for courage, let them really be trying to feel brave. When they say they are praying or forgiveness, let them be trying to feel forgiven. Teach them to estimate the value of each prayer by their success in producing the desired feeling; and never let them suspect how much success or failure of that kinda depends on whether they are well or ill, fresh or tired, at the moment.
But of course the Enemy will not meantime be idle. Whenever there is prayer, there is danger of His own immediate action..."