proselytize vs speak for

proselytize

verb
  • To advertise one’s religious beliefs; to convert (someone) to one’s own faith or religious movement or encourage them to do so. 

  • To coerce into religious conversion. 

  • To advertise a non-religious belief, way of living, cause, point of view, (scientific) hypothesis, social or other position, political party, or other organization; to convince someone to join such a cause or organization or support such a position; to recruit someone. 

speak for

verb
  • To speak on somebody's behalf. 

  • To represent an intrinsic quality 

  • Used other than figuratively or idiomatically: see speak, for. 

  • To claim, reserve, or occupy. 

How often have the words proselytize and speak for occurred in a corpus of books? (source: Google Ngram Viewer )