In The World But Not Of It

What does it mean to be in the world but not of it? How does it make sense in practical, everyday life?  How does it make for a happy, less stressed and more productive life?
Wisdom traditions invite us to explore the idea that we are more than we seem to be. The personality we identify as "me" is a dynamic process rather than a fixed object; a verb as opposed to a noun. 
Those who are of the world dedicate their lives to the pursuit of material things and to reinforcing the idea that the ego is the center of everything.  To them there is nothing else.