Why does an embassy of parishioners visit Mr. Hooper?
An embassy of parishioners is sent to inquire about the veil's explicit meaning because no individual among Mr. Hooper's congregation has had the courage to ask the minister about it directly. The narrator tells us that, despite the fact that there are a number of busybodies in the parish, no one has been able to bring themselves to just come right out and ask the minister why he has begun to wear the black veil. Therefore, the community eventually decides that the best course of action is to send a deputation from the church. Mr. Hooper receives them cordially but grows quiet as he waits for them to explain the reason for their visit; however, in their imaginations, the "piece of crape [...] seemed to hang down before his heart, the symbol of a fearful secret between him and them." They feel that if he were not wearing the veil, they'd be able to ask him about it, but, with the veil hiding his face, they are incapable of broaching the topic at all. They leave having accomplished nothing.
Mr. Hooper is a minister in a small town who shocks the town by appearing one day with a black veil covering his face. The town stands in shock as he enters the crowd. He delivers his sermon, and afterwards his parishioners go home without inviting him to lunch (as is the custom).
Surprising the town again, he performs a funeral still covered by the veil. Then he performs a wedding. The town is outraged. It's not proper for a a minister to hide his face from his people- especially at a wedding.
So, a group is formed to go ask the minister about his new accessory. However, the group finds that once they arrive they cannot ask him about it. The group is tongue tied and so distracted by the veil they cannot achieve their mission.