Psychologists and self-help gurus will all tell us that a grateful heart and a positive outlook will do wonders for health and relationships. A person with a heart of gratitude will be seen by others who will want to follow, and see what he has going for him. Such a person is a magnet for sharing the Gospel, and the greatest source of wisdom has much to say on the subject. Dozens of times in the Bible, we read about the value of gratitude. Paul mentions it several times, including in...