Reverend Hale has a huge background in demonology and witch-hunting, so he is a sought-after expert right from the start. However, Hale is a very dynamic character in the story. At first, he starts off blinded by his own self-confidence. Then he slowly becomes broken into the reality of what really was going in the village. At the end, he was in deep desire of redeeming himself from whatever harm his expertise may have added to the havoc of the village.
As Hale sees the the shady nature of the issue in the village, his self-confidence begins to shatter, and his guilt begins to increase. He goes in a journey of soul-searching, and realizes that the only way to fix things would be to make up for what he may have enabled: To make all the people that he enabled to accuse others to recant their accusations, and try to save those who are now condemned to die. Moreover, he wanted to make witches confess to save them from hanging, although at times he was actively encouraging them to lie. He particularly was feeling guilty for Rebecca Nurse and John Proctor.
Upon being asked why he is back, his answer was
Hale: "Why, it is all simple. i come to do the devil's work. I come to counsel Christians they should belie themselves. There is blood on my head! can not see the blood on my head!!"
However, he is unable to make the people do as he wanted. People would not confess nor believe the promise of being saved by confession. At the end of chapter 4, he does his last attempt at saving his own grace by begging Elizabeth to tell Proctor to change his mind, to no avail. The fact that he even utters the words:
What profit him to bleed? Shall the dust praise him? Shall the worms declare his truth?
Shows that we no longer do we have the boisterous and righteous Hale, but a man that no longer obeys and follows the system. Hence, chapter 4 is the summation of Hale's changes.