mission vs raison d'être

mission

noun
  • A set of tasks that fulfills a purpose or duty; an assignment set by an employer, or by oneself. 

  • Religious evangelism. 

  • An infrequent gathering of religious believers in a parish, usually part of a larger regional event with a central theme. 

  • A number of people appointed to perform any service; a delegation; an embassy. 

  • A settlement or building serving as a base for missionary work. 

  • Third World charities, particularly those which preach as well as provide aid. 

verb
  • To do missionary work, proselytize. 

  • To send on a mission. 

raison d'être

noun
  • Reason for being. The claimed reason for the existence of something or someone; the sole or ultimate purpose of something or someone. 

How often have the words mission and raison d'être occurred in a corpus of books? (source: Google Ngram Viewer )