When we worry, we let our minds wander around from the past to the present to the future, and we wonder or reason about what is going to happen to us, and we lose our peace. God intends for us to keep our minds on what we are doing. I don’t mean to say that we never take time to learn from the past or to make plans for the future. But when we do, it should be something we do purposely, and not the result of a wild mind that never focuses on anything. All these types of thoughts will pressure us, because they are not God’s will. The prophet Isaiah said that God would keep us in perfect peace when our mind is fixed on Him.
You will guard him and keep him in perfect and constant peace whose mind [both its inclination and its character] is stayed on You, because he commits himself to You, leans on You, and hopes confidently in You.
The writer of Proverbs stated that the good man would be satisfied with “[the fruit of] his ways [with the holy thoughts and actions which his heart prompts and in which he delights]” (Proverbs 14:14).
Do you want to be peaceful, guarded by God, and satisfied? Then you need to realize that it begins with the thoughts that you choose to think. Your mind is connected to every feeling you have and every action that you take.
If you give yourself over to worry and reasoning, your thoughts may sound like this: How am I going to do everything I have to do? My life is impossible! This is more than I can handle. Instead of worrying about the future, you could think things like: God loves me, and He will take care of everything in my future. He will give me the strength and ability to do each thing I need to do as it comes up.
Excerpt from The Mind Connection: How the Thoughts You Choose Affect Your Mood, Behavior, and Decisions by Joyce Meyer