baptism vs introduction

baptism

noun
  • A similar ceremony of initiation, purification or naming. 

  • A Christian sacrament, by which one is received into a church and sometimes given a name, generally involving the candidate to be anointed with or submerged in water. 

introduction

noun
  • The act or process of introducing. 

  • A written or oral explanation of what constitutes the basis of an issue. 

  • A means, such as a personal letter, of presenting one person to another. 

  • An initial section of a book or article, which introduces the subject material. 

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