There is so much depth and truth in this quote, people can only understand it if they are open-minded. It means that a believer has many duties in this life, so many burdens and issues in this less-than-perfect world which he is constantly trying to combat. This is due to the Islamic principles which ensure he acts righteously for the benefit of humanity. However, non-believers do not always feel the same amount of responsibility and are often too busy with the enjoyment of their luxuries - thus it is a paradise for them because they are oblivious to the hurt and suffering of others.