Psalm 34:13-14

Keep your tongue from evil and your lips from speaking deceit. Turn away from evil and do good; seek peace and pursue it.  

We exercise our authority in our lives by what comes out of our mouths. If we think evil, we will speak evil and work toward deceit which robs us of our peace. Peace comes to our lives because we pursue what is good and holy. Peace is something we must pursue by controlling our thoughts and avoiding evil.