Isaiah 26v3 You will keep in perfect peace him whose mind is steadfast, because he trusts in you. 4 Trust in the Lord forever, for the Lord is the Rock eternal.
Our thoughts make us who we are. If we focus on the joy and truth found in Christ we will have peace. So take control of every thought and when the devil tries to speak deceit, discouraging lies RECOGNIZE it, and think of the victory in Christ. Forget the struggle remember the victory.
2 Corinthians 10v5 We demolish arguments and every pretension that sets itself up against the knowledge of God, and we take captive every thought to make it obedient to Christ.