Philippians 4:8

Finally, brethren, whatever things are true, whatever things are noble, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthy-meditate on the things.

Our thought life should be managed and controlled. Not every thought that wanders through our minds should be allowed because we know the devil will send stray, stupid thoughts to take us off course. When we meditate on what is lovely and true, that is what we speak over our lives. Our lives then produce what good things we think and speak.