I am convinced that there is one KEY to happiness, and that is PURPOSE. Living for a purpose greater than ourselves. If and when we spend most all our time focused on ourselves we grow more and more depressed, but when we can forget about ourselves (for the most part) and focus on helping others, or serving a greater purpose ... we have JOY!
Christ gives meaning to an otherwise meaningless existence!
John 10:10b Jesus said, "... I have come that you may have life and have it to the full."
John 14:27 "Peace I leave with you; my peace I give you. I do not give to you as the world gives. Do not let your hearts be troubled and do not be afraid."