Finally, brothers, whatever is true, whatever is honorable, whatever is just, whatever is pure, whatever is lovely, whatever is commendable, if there is any excellence, if there is anything worthy of praise, think about these things. - Philippians 4:8
How you think affects every area of your life. If you allow negative thoughts to fill your mind, you become a negative person. If you fill your mind with positive thoughts, you become a positive person. This promise invites you to focus your mind on the good and positive things in life.
Proverbs 23:7 says you become what you think on. Paul encourages us to think about the positive.