You’ve probably heard you should exercise. Exercise is a law of radiant health. Regular exercise improves and sustains your well-being and comes with many wonderful benefits.

But guess what? Many, many people exercise for the wrong reason!

To discern what that reason is, think about this basic truth. There are two ways of life: give and get. God’s way and Satan’s way. God’s way is outflowing—Satan’s is incoming. God’s is concern for others—Satan’s is concern for self. God’s way is love—Satan’s way is vanity.

Some things are obviously the way of get: abusing alcohol, taking drugs, gluttony, arrogant trash talk. Other things require true discernment to recognize the difference. Music can be uplifting and godly—or satanic. A positive hobby can turn into an unhealthy obsession. A person might perform a helpful service but with selfish motives. You may do the “right thing”—but for utterly wrong reasons that actually express vanity.

For many people, exercise is vanity. Society exalts and worships sports stars for their physical skills regardless of the depravity of their morals and character. People become unwholesomely fixated on personal fitness. Doggedly chasing greater speed, skill or strength, teens and adults grow intensely focused on themselves at the obvious expense of God and other people.

One of the biggest traps Satan sets for us is to fix our attention on physical looks. People around you unashamedly focus on body image in a spectacular multitude of unhealthy ways. Airbrushed images are everywhere of what you are “supposed” to look like—causing many to be dissatisfied with normal. Many people hate aspects of their appearance—the way God made them—simply because they don’t match certain societal standards of beauty or handsomeness.

Being healthier does tend to be more attractive, and efforts to improve your health can enhance your attractiveness. But many of the models of human bodies that are being glorified have no correlation with health, and trying to live up to them is preposterous. Many people value thinness or bulkiness over health. They diet, they starve, they get eating disorders. They train for looks rather than functionality. They preen and flex and even take pictures of themselves in the mirror. They take drugs, they go under the knife to remove fat or stretch skin, they inject themselves with poisons, they insert implants—whatever it takes to achieve that look.

Vanity is sin, and this world is loaded with it. So much of that vanity revolves around appearance. The unhappy evidence of Satan’s thinking is all around us. Is it possible his errors and lies, his vanity, have affected your thinking? Be honest. It can afflict you in ways you probably don’t realize and might not want to admit.

Here is God’s condemnation of Lucifer: “Thine heart was lifted up because of thy beauty” (Ezekiel 28:17). It is easy for human beings to fall into the same trap, especially because Satan is actively trying to pull us into it.

You do need to exercise! But don’t exercise so you can admire yourself in the mirror. Don’t do it so you can look better at the pool. Don’t do it to stoke your vanity. You already have too much vanity! This is a perspective we cannot afford to forget, though it is very easy to do so: This physical life—everything we work for, get excited about, pour our energies into and get emotionally worked up over—is vanity if it is not connected to our spiritual purpose (Ecclesiastes 1:2-3). Exercise, sports, World Cup soccer, the nba, coffee, the Food Network, haute cuisine, the latest movie, literature, music—whatever it is, in and of itself, it doesn’t amount to anything!

You are not on Earth for long. Physical things have the illusion of permanence. It is especially common for young people to act like these physical things will last forever. But they don’t—and that is certainly true of physical strength and beauty. Just ask the former pageant queen now in her 60s or the gifted athlete who sustains a career-ending injury in a split second.

Your body is temporary—it is a tabernacle, a temporary dwelling. Like grass, it sprouts up, looks nice for a short season, then gets mowed down and returns to dust (1 Peter 1:24). Despite that truth, however, many get caught up in the vanity of building their bodies. Some practically worship these physical bodies! That is pitiful and ridiculous. God gave us our bodies for a purpose: to provide us the opportunity to build spiritual character.

Everything we do, we must put in the context of what God wants to accomplish with us spiritually. Is it helping you grow in character? Is it serving others? Does it advance God’s Work? Is it leading to eternal life? Will it help you gain a greater eternal reward? If not, it really is vanity—and you need to look seriously at cutting it out, or at least making sure it fits snugly into a very tiny corner of your thinking and your life.

Never lose this perspective from 1 Timothy 4:8 (Revised Standard Version): “[W]hile bodily training [or exercise] is of some value, godliness is of value in every way, as it holds promise for the present life and also for the life to come.”

So when you exercise, check yourself in the figurative mirror—and make sure you’re doing it for the right reasons!