I believe the theme is laugh at every opportunity: laugh every day. Man has struggled since the beginning of time, and what remains is laughter. It has been here since the stars were created. It has been a part of man's experience from his first day.
With all that comes in the living of one's life, laughter is the thing that matters most. So the author advises all to laugh with friends and be merry whenever possible. Laugh with the array of nature laid out before you. Laugh with your brothers as long as life give you the opportunity to experience the world's joy.
And continue to laugh as long as life goes on, until the dances are done, the music ends: "laugh till the game is played:" until life is over.