Since the devil knows what strength, comfort, and benefit may be derived from prayer, he uses all the power and subtlety at his disposal either to keep you from praying or to trouble you while praying.
(1) He will suggest as many other activities to you as he possibly can, divert your thoughts elsewhere, and induce you to postpone prayer to a given time (having something else to do first).
(2) Sometimes he suggests that prayer is a work so difficult that you cannot do, are entirely unfit for, are presently in too sinful a condition, and that you should thus wait for a season when you will be more fit for it.
(3) Sometimes he gives a deep impression that prayer is both ineffective and fruitless.
(4) Sometimes the devil, as if throwing in a handful of dust, is also busy casting other thoughts into our minds while we are praying (IV: 239-240).