"It is our ability to deal with challenges and not their absence that gives us their true glory, comfort and happiness in life" simply means that the absence of challenges is not directly proportional to glory, comfort and happiness in life. It doesn't that if you do not have struggles or problems in life you are happy because the challenges and the pain we got from fighting those challenges are the sole reason that we recognize the blessing of happiness and comfort. Without the challenges and struggles we would not be able to know and value the gift of life, the happiness and everything in the world.
