"Either make the tree good, and his fruit good; or else make the tree corrupt, and his fruit corrupt: for the tree is known by his fruit" -- Matthew 12:33
For the believer, right thinking is something that is so important that one simply cannot live without it -- like a heartbeat is vital, or blood pressure is vital. There are things without which there is no life. Our life source, our source for right thinking, is regular, personal fellowship with Heavenly Father in prayer and regular study of his Word found in the standard works.
The Bible says that a tree is known by its fruit.
The same is true of our lives. Thoughts bear fruit. Think good thoughts, and the fruit of your life will be good. Think bad thoughts, and the fruit in your life will be bad.
Actually, you can look at a person's attitude and know what kind of thinking is prevalent in his life. A sweet, kind person does not have mean, vindictive thoughts. By the same token, a truly evil person does not have good, loving thoughts.
Remember Proverbs 23:7 "For as he thinketh in his heart, so is he:"
As Mom pointed out in her blog today, our appearance also reflects our thoughts. When we present ourselves civilly we show others respect. When we take the time to make ourselves lovely for worship each Sabbath we are showing respect for our Heavenly Father.