John Hale was brought to Salem to cleanse the town of the devil. Hale quits the court in Act 3 because he no longer believes that the girls are telling the truth and feels that the judges are blind to the lies that they are telling.
John Proctor is not successful in convincing the court of his affair with Abigail; since Hale knows what kind of a person Proctor is, he now truly believes that he is being truthful and that the girls are fabricating the entire story. Therefore, he quits the court. Hale continues to play a part in the play when he tries to convince certain characters to confess to witchcraft only because he does not wish to see them hanged.
Towards the end of The Crucible, Abigail tries be rid of Hale by going to Judge Danforth and saying she saw Rev. Hale's wife with the devil.