Paul wrote the book of Philippians after he had been in jail between two and five years. Yet, 17 times in that letter Paul used the words "joy" or "rejoice." Paul's joy was independent of his circumstances. In this letter to the Philippians, Paul shares the basis of his unshakable joy. For him, life was Jesus, and death was even better because it would bring him closer to Jesus. Death to self is the only way to life and happiness.
From CD Set: How to be Happy - 1019C