There are many theories in literature trying to answer the ONE question that Hawthorne never really addresses: Why did Mr. Hooper do this?
While the story points at a similar event that took place in real life, the Mr. Hooper of our story is too enigmatic to answer the question, or even hint at an answer. He even drives his fiancée away and scares everyone off. Since this behavior is odd at most, let's look at the different hypotheses that have been in the air regarding this.
1. Mr.Hooper is a champ at making his points:
One theory is that Mr.Hooper is adamant in making a point about showing how people hide their true selves in plan view of others, making us all hypocrites by default. The veil of the minister represents the hidden world that all of us put away behind a safe and acceptable façade. Similarly, none of us really knows what lurks beneath the surface of those whom we think we know best.
Mr. Hooper's willingness to make these points represents a mission that goes beyond himself. It is a calling that he feels drawn to and, as such, he is willing to sacrifice everything that he has known thus far for the mere sake of doing what he feels he must do.
2. Generativity vs. Stagnation: Mr. Hooper's inner psychology
In the field of human development, particularly during the stage 7 of Ericksonian psychology, known as Generativity vs. Stagnation, it is theorized that once or twice in our adult lives we experience a need to be a part of, conquer, or be taken to, what is known as "the rock that is higher than us". This is a tendency in adults about to reach middle age, or even as we enter our senior years, to want to do something truly spectacular, historic, heroic, or just grand enough to make into a personal milestone. It is the proverbial "before I die I must..." dictum.
Arguably, this moment hit the young, intelligent minister during a time in his life where he was in a position to being of help to others. Hence, this desire to achieve something huge, and to be closer to that "which is higher than himself" came exactly during a time when he had already established other milestones, such as being engaged, and being a respectable member of society.
3. Mr. Hooper is a doppelganger of Hawthorne
Like Nathaniel Hawthorne himself, Mr. Hooper was eccentric and not too fond of people. We could throw in two funny cents and argue that Mr. Hooper did what Hawthorne would have wanted to do if given the chance: be gone from public view. Maybe Hawthorne, to a point, crafted this character after himself and just added the veil to add artistic license to an already controversial story.
4. Mr. Hooper is a masochist.
Many religious sects and groups place immense importance in the willingness of a member to engage in self-sacrifice. These sacrifices have been witnessed in history in many dimensions, from self-flagellation, to starvation, and much more. A veil is not as outrageous as the other options, but it is certainly extreme from a social standpoint.
As part of a sacrifice, he would leave behind all that he loves and/or needs. The pain is part of the process of purification of the soul. All of this is theoretical and based on theological perspectives, but it could serve as a possibility.