Most people can relate to the character of Proctor because of his conflicts with himself. John is torn between the love for his wife, Elizabeth, and his mistress, Abigail. He knows it is wrong to commit adultery and he refuses to continue to hurt his good wife with the elicit affair, but he wants to keep this betrayal at home and not public in court. John is paying his dues with Elizabeth and he does not want it to come under public scrutiny. This is something many of us can sympathize with. John is also struggling with his religious beliefs. He sees the corruption found in the religion and he wonders if breaking away from the community will help to save the sanctities of his family. This is something else that most of us can relate to now matter the time period.
John Proctor is of course conflicted because he still has feelings for Abigail, feelings which he denied himself ("I will cut off my hand before I reach for you again"). He also feels guilty because of his religious convictions against adultery, and the strains it has put on his family life.
To make this public in the court, as he decides to later, is more than a confession, it is destroying his reputation and he knows it. So in a way, he may have felt it was a sort of penance, for lack of a better word, for his sins. Once the truth is made public about his relationship with Abigail, there is no going back, his good name and reputation are damaged permanently, but he seems not to truly care in the end, because the world has gone mad for him. Because he would much rather he himself lost his reputation or be put to death as opposed to his wife bearing the weight of the accusations put forth by Abigail, accusations he knew to be false, with only one way to prove it so.
In a way, his confession and loss of reputation redeems him.