In The Crucible, Reverend Hale is brought in as an expert on witchcraft. His job is to investigate the claims and interview all those involved. Hale takes this work very seriously and he intends to rid Salem of any instances of witchcraft. Hale does, however, go about his business with much more reason and calm than the fanatics who embrace the hysteria of the accusations of witchcraft.
In Act IV, we see the dynamic character of Reverend Hale. After trying to coerce more confessions (along with Parris), Hale reverses his stance and asks Danforth to pardon those who've been condemned (Danforth does not do this). Hale then actually tries to get the confessed to lie in order to save their own lives.
Hale represents the dichotomy of the witch trials. He is a part of the hysteria but he is also one of the characters who actually shows a reasonable, rather than a fanatic, conscience. Toward the end of Act IV, Hale begins to see the devastation of the accusations and his part in it:
Why, it is all simple. I come to do the Devil's work. I come to counsel Christians they should belie themselves. His sarcasm collapses. There is blood on my head! Can you not see the blood on my head!!
Shortly after this, Hale asks Elizabeth to get John to confess to save his own life. Hale is trying to do the right thing but he also feels guilty and if John is to be executed, Hale would feel responsible and acknowledges this responsibility to Elizabeth.