The joy of life comes from our encounters with new experiences, and hence there is no greater joy than to have an endlessly changing horizon, for each day to have a new and different sun.

This quote is saying that life is most enjoyable when we experience new things. Having variety and change in your life is the source of true joy. A new horizon each day gives us a chance for a fresh start and offers a different perspective. Just like the sun rising on a new day, the possibilities and opportunities for happiness are endless.