I hate massive generalisations as you know, but...
Bertrand Russell, polemicist, atheist philosopher and author of 'The Pursuit of Happiness'
The atheist is concerned primarily with what will make him happy. He is concerned with his happiness and finds but a fraction of it.
The Christian is primarily concerned with what will make God happy. She is concerned with His Happiness and finds it in its fullness.
Blessed Teresa of Calcutta