In Act IV of The Crucible, what is Hale's mission?
Hale's mission in Act IV is to ensure that innocent people aren't put to death. By this point, he has seen enough spectral evidence to know that the girls are faking it, and he has heard enough testimony in and out of the courtroom to know that the people who are on trial are not deserving of the punishment they are about to receive for the crime they did not commit.
This is different because prior to his opportunity to get to know these people after their duration in jail, he was just like everyone else, ready to see these people hung and believe that they were witches just because someone else said so. Hale came to the town as an expert in the field, and here he has had no success, and it changed him.