Proctor goes through a transformation of character, retrieving his dignity back from the scandal of his adulterous affair with Abigail. More than that, he is renewed in his faith, realizing that the only way to save himself from true evil is to resist the temptation to lie to save his life. He surrenders his life to save his soul.
He literally reclaims his soul when he decides to tear up the confession. This is evidenced by his wife's final comments in the play.
"Elizabeth: He have his goodness now, God forbid I take it from him!" (Miller)
John confessed in order to save his life. His wife was expecting, and he thought it best to lie in order to be around for his family. After his confession, he is urged to sign. At this request, he begins to have reservations, and he responds, "Because it is my name! Because I cannot have another in my life! Because I lie and sign myself to lies! Because I am not worth the dust on the feet of them that hang! How may I live without my name? I have given you my soul, leave me my name!" Despite his reservations, he signs the confession.
Then, he hears that Giles Corey refused to answer the charge and died by being pressed to death. The straw that broke the camel's back is when Rebecca is brought in. She also refused to confess and will be hanged as a witch. John realizes that honor is more important. He also decides to stop living a sinful life of lies and become a better person. He refuses to play the evil game by naming others and tears up his false confession. Elizabeth is urged to try to persuade him, but she refuses and understands his need for redemption.
In Act IV of "The Crucible", John decides to rip up his signed confession for two reasons. First, after the confession is signed, Danforth tells one of his court marshals to hang it on the church door so that john can be used as an example to the people who refuse to confess to witchcraft. Once John realizes this he decides that John Proctor will not be used as an example of someone who lies to save his life and, therefore, takes his confession back. The second reason is that John realizes that signing this confession will ruin his name for his three sons. His reasoning is, "Because it is my name." He takes back the confession for those two reasons.