This statement related to the central theme of the novel: Happiness and contentment can only be achieved by concentrating on peace and well-being within one's self, rather than seeking adventures/riches/material goods to manufacture happiness.
Throughout his life, Candide has struggled with Pangloss' philosophy of optimism, attempting to reconcile what he's been taught with what he sees before him. How to explain war, murder, starvation, rape, poverty, etc., when one's philosophy holds that "everything is for the best in the best of all possible worlds"? It is only at the end, when Candide meets the old man who is happy on his farm, that he realizes one can only be content with those around them if they are striving to achieve happiness within, rather than without. All of the futile attempts to gain happiness through riches, religion, marriage, etc., have all failed. Instead, Candide combines the teachings of his two influences, Pangloss and Martin, to a belief in the power of a simple life, a life that can bring true inner contentment.