Daily movement and exercise are essential to a healthy immune system. Unlike the heart, which pumps blood, the lymph system has no pump and relies solely on bodily movement to do its work of feeding cells with nutrients, clearing cell waste, and filtering out germs. Without daily exercise, cell walls become compromised and more easily admit foreign substances such as viruses. Daily exercise is also needed to prevent dementia. Americans have grown lazy, spending too much time indoors and on their rears, neglecting exercise along with proper nutrition and water, and looking for quick fixes instead of putting in the effort. God has given us a body fully capable of protecting itself, provided we do our part to keep it healthy, and He does not bless lazy and poor stewards. Caring for the body through exercise is therefore a matter of stewardship of the God-given immune system, and improper care carries both spiritual and physical ramifications. When we do our part, the body's terrain becomes inhospitable to viruses. Even so, we must trust our Creator, since we may still get sick and need His healing.

Too little exercise is one element of the national health problem, alongside too much sugar, salt, refined grains, meat, fat, and alcohol, and too little fresh produce, whole grains, pure water, and self-control. The result is widespread obesity, which directly causes some twenty diseases, several of them major. Physical health matters because the physical and spiritual aspects of life affect each other, and a body in good condition is better prepared to give godly love rather than dwelling on itself. Caring for the body is a matter of physical morality and a duty, in keeping with Paul's charge to glorify God in body and spirit, since believers were bought at a price (I Corinthians 6:20). Self-control, a fruit of God's Spirit (Galatians 5:23), applies to the disciplined habits that produce good health. Improvement requires rethinking one's attitude, rejecting the idea that poor ancestry makes change impossible, learning general health principles and one's own particular tolerances, and patiently persisting, since recovering what has been lost may take years.

Exercise, along with diet and other natural methods, is the most effective way to treat and prevent disease. The Hippocratic school of ancient Greece attached great importance to diet, and in chronic cases it relied chiefly on diet, exercise, and natural methods, treating medicines as secondary. Ancient physicians recognized the vital importance of healthy living in preventing disease, and a doctor's primary duty should be to teach people how to live healthfully rather than to cure them after they become sick.