It is clear why Reverend Hale was such a strong supporter of the court at first. He came to Salem believing firmly in the reality of witches and their powers, the common wisdom of his day. He brought with him many "scientific" books to help him in his attempt to discover whether witchcraft was being practiced in the community. His intention was to help. If he found witches in Salem, he intended to free those who had been bewitched to save their souls. Once Hale becomes convinced that the Devil is present in Salem, he works hard to do just that.
After Hale realizes that Abigail is a fraud and that the trials are "vengeance," he makes an emotional appeal for the accused, quits the court, then leaves Salem feeling enormous guilt: "There is blood on my hands!" At the end of the play, Hale returns to save those about to hang by trying to convince them to lie and go free. He has agonized over his role in the tragedy. He tries valiantly to undo whatever damage he can while there is still time.
I understand why Hale acted the way that he did in the beginning of the play. He comes to Salem armed with both his beliefs and his knowledge, provided by his many books, of how to cleanse a witch, how to identify a witch, and so on. He really has good intentions, his source is actually the bible, he is using the good book as the basis of his belief that witches exist in the world.
Reverend Hale might be a little naive about the presence of evil in the world, as a man of God, he knows that there is evil, but maybe in the beginning he can't identify it.
At the end of "The Crucible," Reverend Hale is a man consumed with guilty purpose. He has contributed to the deaths of many innocent people. As a man of God, he seeks inspiration and forgiveness from God. Although he is unsucessful in his quest to save John Proctor, Reverend Hale emerges with a greater understanding of the nature of evil and where to find it, how to identify it.
He has witnessed the corruption of Danforth and the other judges as they attempt to protect themselves from scrutiny after they ordered innocent people to be executed. Hale has truly seen the face of evil.