Some scholars believe C.S. Lewis to be one of the most spiritual writers, outside of the prophets, who ever lived. Certainl the above quote is evidence of that.
When we look for happiness and peace outside of God, we're looking in the wrong place. It's like that old song, "Looking for love in all the wrong places ..." I've looked for happiness and peace in material possessions. I've looked for them in worldl achivements. I've looked for them in food.
None of those brought happiness. None of those brought peace. And, certainly, none of them brought joy.
This I know for sure: happiness and peace are inextricably tied with God and letting Him into our lives.