The Bible says in Proverbs 3:27, "as a man thinks in his heart, so is he." You will eventually become what you think. And you can't think one thing and become something else. If you allow yourself to think negative worried, fearful thoughts, then you will become a negative, worried, fearful person. You cannot think defeat and expect victory. You can't think poverty, and expect wealth. You can't think the worst, and expect the best.
You've got to be extremely careful and extremely aware about what you allow your mind to think about. And what you choose to dwell on.
Fear is a force just like faith is a force. If you give into fear and start to dwell on that junk and start to act on it, that fear can actually bring things to pass just like faith can bring things to pass. Job said, "the thing I greatly feared came upon me."
The Bible tells us what we should dwell on in Philippians 4:8. It's to "think on things that are pure and honest and of a good report." Things that build you up, not tear you down. Think on all the great things God has done for you, the bible says. In other words, you've got to dwell on the positive and not the negative. Quit thinking about what you don't have and start thinking about what you do have. Quit thinking about what's wrong with you and start thinking about what's right with you. Quit thinking about how big your problem is and start dwelling on the fact of how big your God is.
See, we've got to learn to live a grateful life and we've got to always focus on the positive and not the negative. If you're continually thinking about the goodness of God, you're not going to have any time to worry and complain and get down and discouraged. If you're always meditating on God's promises, then you're always going to be filled with a good report. The words that come out of your mouth are going to be faith-filled words.
Exerpts from Guarding Your Thoughts -- Joel Osteen