Answer:
The quote is a form of indirect characterization, it means that Proctor is sinful, a sinner against the moral laws of the Puritans and against his own vision of what he should be like.
Explanation:
The quote that you provided is one piece of the puzzle, but the quote is further helped a few lines earlier with the following:
"He is a sinner, a sinner not only against his moral fashion of the time but against his own vision of decent conduct."
John is a sinner against the moral fashion of the time, because he had an affair with Abigail Williams. John is a sinner against his own vision of decent conduct, because he knows what he did, but nobody else knows. He is held in high regard by everyone in Salem, but he believes it is a falsity. In a way, John feels as if he is lying to everybody about his goodness. He feels like a hypocrite, which is why Miller writes that John was a sinner "against his own vision of decent conduct."
