Set your mind on things above, not on things on the earth.
For you died, and your life is hidden with Christ in God."
Colossians 3:1-3 (NKJV)
If you want to develop your muscles, you need to exercise. But, to properly exercise your muscles, you need to do the right kinds of exercise. For example, if you wanted to strengthen your legs, you would not do pushups. If you needed to develop your cardiovascular system, you would not do exercises that are just for your arms. By doing the right exercises you can develop and strengthen your body. If you do not do any exercise, you are actually still making an impact on your body, it is just that the impact will be a negative one.
The Bible says a lot about the mind and our thinking. The Bible talks about renewing the mind (Romans 12:2) and the right kinds of things to think about (Philippians 4:8). Unfortunately, this is an area that many Christians have not paid the proper amount of attention to. If we do not renew our mind and think about the right things, this can lead to other problems, because our thinking and believing are connected. You cannot believe something you have not thought about, and you will think about the things that you believe.
Colossians 3:2 tells us to "set our minds on things above", which is talking about what we think. To "set your mind" can be defined as, "to exercise the mind". If we think about spiritual truth, we will exercise and develop our mind, just like by doing certain exercises we would develop our body. Rather than just struggling with wrong thoughts, depression, and stress, we can have a stronger mind through continually thinking about godly things rather than earthly things. Start exercising your mind today by thinking about God's Word, and you can develop a strong thought life.