free grace vs invocation

free grace

noun
  • A concept of grace as a gift given freely by God, without regard to entitlement or merit. 

invocation

noun
  • The act or form of calling for the assistance or presence of some superior being, especially prayer offered to a divine being. 

  • The act of invoking, such as a function call. 

  • A call or summons, especially a judicial call, demand, or order. 

  • An act of invoking or claiming a legal right. 

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