Put on the full armor of God that you may be able to stand against the wiles of the devil...above all, taking the shield of faith with which you can quench all the flaming darts of the evil one. (Eph. 6:11,16)

Using the shield of faith means refusing to accept thoughts which contradict the truth. We thus bring God's power on the scene. When attacked, Jesus put up His shield by quoting God's Word, and Satan's darts bounced right off. Lies have no power over someone who knows the truth. God has given us His mighty armor, but we must put it on by reading and meditating on His Word. Only those who know the truth can recognize which incoming thoughts are flaming darts hurled by the enemy.
 

Lying to my daughter

To train her in spiritual warfare, I sometimes lie to my 6 year old, Jennifer. As my finger shoots toward her stomach, I say, "God has left you, Jenny! He's not with you anymore." Fortunately, Jenny is prepared for her Dad's weird game. Blocking the dart with her hand, she responds, "It is written, 'I will never leave you nor forsake you.'" I press on with the attack, "But you don't feel His presence, do you?" She responds, "What difference does that make? God said, "I'll never leave you nor forsake you."

I try another lie. "Satan has good things for you, Jenny! He wants you to have fun." She again blocks the dart with her hand and says, "It is written, 'The thief comes only to steal, kill, and destroy.'"

God wants us to be free indeed on the inside. His truth will not only make us free; if we use it as a shield, it will keep us free.