What is the theme in The Greatest Miracle in the World by Og Mandino?

One of the basic elements of this book is friendship. Og was a busy man who worked hard at his job and had a successful book at the same time. Og was always running off to meetings or promotional tours for his book and never had time to sit and do nothing until he met Simon Potter. Simon Potter changed Og's life, giving him a reason to just sit and do nothing. The two men met on a snowy day when Simon offered to help Og with the gate at the parking lot where he parked while at his office. Months later, Simon invited Og to have a sherry at his apartment. Soon the two men were spending most evenings together, sharing a drink and talking about things as simple as their own lives and the complicated philosophies of some the world's greatest writers. Before Og realized, a friendship had arisen.