Sentence:  And further he must understand his <WSD>obligation</WSD> to the client to not only meet his physical necessities but also to enhance and improve his life and to enlarge the cultural horizon of our society . 
Meaning of the word marked with <WSD> tags:  the social force that binds you to the courses of action demanded by that force; every opportunity, an obligation; every possession, a duty"- John D.Rockefeller Jr