Why do Rebecca Nurse and Giles Corey's fates affect John Proctor powerfully?

John Proctor has a lot of respect, admiration, and liking for both Rebecca Nurse and Giles Corey. They all share varying degrees of dislike for Reverend Parris and are initially suspicious that the girls are behaving disingenuously when they make their accusations.
When Rebecca Nurse chooses execution instead of giving a false confession to save her life, John admires her deep faith and personal integrity. Rebecca will not commit the sin of lying or turning her back on her religion because she cares more about her eternal life than her earthly one. When John is considering a false confession to save his own life, he ultimately finds he cannot do it, but he refuses to think of himself as being on the same moral plane as her. He knows he is flawed, while he sees no fault in her.  
John's feelings about Giles Corey are similar. Giles will neither enter a plea nor give up the name of the person who heard Putnam tell his daughter to accuse George Jacobs because Giles believes that to do so would lend credibility or legitimacy to the trials. By remaining silent he takes a moral stand, and like Rebecca, Giles will not give a false confession to save himself from execution.
Though he is younger than them and has two children and a pregnant wife, John's ultimate decision is to emulate their behavior, perhaps finding in it some personal redemption.