"Thus also the devil is angry because God wants to trample him under foot by means of flesh and blood. If a mighty spirit were opposed to him, he would not be so sorely vexed; but it greatly angers him that a poor worm of the dust, a fragile earthen vessel defies him, a weak vessel against a mighty prince. God has placed his treasure, says St. Paul, in a poor, weak vessel; for man is weak, easily aroused to anger, avaricious, arrogant, and weighed down with other imperfections, through which Satan easily shatters the earthen vessel; for if God would permit him, he would soon have utterly destroyed the whole vessel."
Sermons of Martin Luther, 8 vols., ed., John Nicholaus Lenker, Grand Rapids: Baker Book House, 1983, V, p. 268. Twenty-first Sunday after Trinity, John 4:46-54; 1 Peter 5:8; Ephesians 6:12.