"Put on the whole armor of God, that you may be able to stand against the schemes of the devil. For we do not wrestle against flesh and blood, but against the rulers, against the authorities, against the cosmic powers over this present darkness, against the spiritual forces of evil in the heavenly places. Therefore take up the whole armor of God, that you may be able to withstand in the evil day, and having done all, to stand firm. Stand therefore, having fastened on the belt of truth, and having put on the breastplate of righteousness, and, as shoes for your feet, having put on the readiness given by the gospel of peace. In all circumstances take up the shield of faith, with which you can extinguish all the flaming darts of the evil one; and take the helmet of salvation, and the sword of the Spirit, which is the word of God . . ."Paul tells us in Ephesians 6:10 to "be strong," but he tells us to be strong in the Lord's might, not ours, which is why before we get to praying and making supplication, we are to put on the armor of God. Notice that this armor consists entirely of things God does or provides for us. We don't put on the helmet of self-affirmation. We don't put on the shoes of motivation. We don't put on the belt of intestinal fortitude. No, we put on what God has done for us in Christ, which is to say, we put on Christ.
-- Ephesians 6:11-17
When the enemy attacks my heart, I don't want my self-righteousness standing guard, but the breastplate of actual righteousness, Christ's righteousness. When the enemy whispers his accusations into my ear with his forked tongue, I don't want Stuart Smalley-esque daily affirmations sitting there; those would protect me about as much as cotton-ball earmuffs. But the helmet of salvation is another story. If my mind is ready with the great salvation of the gospel encasing it like a force-field of grace, I am really prepared.
Which is why we must wear this armor constantly. We should never take it off. We should wear it to bed as pajamas. We should make sure we've got it on first thing in the morning by turning to the gospel as immediately as possible. This is wartime. Don't take the armor off. You don't try putting on your seatbelt when you see the Mack truck bearing down on you at 60 mph; you put it on before you pull out of the garage. Likewise, don't wait for the enemy to show himself before you start suiting up.
You don't know when the attacks will come; best to sleep with your boots on and your sword by your hand.