Do not be wise in your own eyes;
Fear the Lord and depart from evil.
It will be health to your flesh,
And strength to your bones.
Satan’s deceptive cunning is highlighted by Paul’s statement that he becomes an angel of light, disguising evil as good (2 Cor. 11:14). His destructive ferocity comes out in the description of him as a roaring, devouring lion (1 Pet. 5:8) and as a dragon (Rev. 12:9). As he was Christ’s sworn foe (Matt. 4:1-11; 16:23; Luke 4:13; John 14:30; cf. Luke 22:3, 53), so now he is the Christian’s, always probing for weaknesses, misdirecting strengths, and undermining faith, hope, and character (Luke 22:32; 2 Cor. 2:11; 11:3-15; Eph. 6:16). He should be taken seriously, for malice and cunning make him fearsome; yet not so seriously as to provoke abject terror of him, for he is a beaten enemy. Satan is stronger than we are, but Christ has triumphed over Satan (Matt. 12:29), and Christian’s will triumph over him too if they resist him with the resources that Christ supplies (Eph. 6:10-13; James 4:7; 1 Pet. 5:9-10, 1 John 4:4).
Acknowledging Satan’s reality, taking his opposition seriously, noting his strategy (anything, provided it be not biblical Christianity), and reckoning on always being at war with him-this is not a lapse into a dualistic concept of two gods, one good, one evil, fighting it out. Satan is a creature, superhuman but not divine; he has much knowledge and power, but he is neither omniscient nor omnipotent; he can move around in ways that humans cannot, but he is not omnipresent; and he is an already defeated rebel, having no more power than God allows him and being destined for the lake of fire (Rev. 20:10).
Commentary from, Concise Theology, by J. I. Packer, page 70.
“Our business is to get them away from the eternal, and from the Present. With this in view, we sometimes tempt a human (say a widow or a scholar) to live in the Past. But this is of limited value, for they have some real knowledge of the past and it has a determinate nature and, to that extent, resembles eternity. It is far better to make them live in the Future.” The Screwtape Letters, by C. S. Lewis, page 76/chap. 15.