The works of Sa'di from beginning to end teach the first lesson of faith, which is to understand that we are not here in this world in vain, to waste our lives. We are here for a purpose, everyone for a particular purpose. Each one of us is an atom of this universe and completes the symphony, and when we do not strike our note it means that note is lacking in the symphony of the whole. When we do not fulfilled our life's purpose in the way for which we were created we are not living rightly and consequently we are not happy.