Like produces like. Good produces good. If our all day thinking is positive, constructive, kindly, we produce health, success, and freedom. If our hour-to-hour thinking is negative, pessimistic, mean, we produce sickness, failure, and unhappiness. If our life is governed by Faith we become younger, more prosperous, and more joyous, as the years pass. If our life is governed by fear, the fleeting years bring age, decrepitude, and frustration.
Spiritual growth comes from putting into practice the knowledge we already possess. Instead of reading another book, read your favorite book once more and apply it more carefully than ever in your practical life.