Father Hooper wears a black veil over his eyes and nose, never revealing the reason of the veil to a soul. At times the sexton would insinuate a reason behind the veil but never revealing the answer to the mystery. Father Hooper is a very imaginative and creative individual to innovate the idea of wearing a black veil to express an idea. He is angry towards the response of the veil to his parishioners, since they treated him differently with the veil compared to without it. Most of the parishioners are clueless to why he wears it and some try to imagine why he would ever want to wear it, but there are only ideas and arguments to why a minister would wear it. One of the reasons behind the veil might be secret sin. Father Hooper might have committed a very bad sin which he does not want to unveil to anyone.
Instead of not telling anyone the sin he shows it clearly on his face with the aid of a black veil. This black veil might relieve tension in his body that has accumulated due to his sin. In the story, Father Hooper says that everyone wears a black veil, meaning that everyone commits secret sins without revealing them to anyone. If you do not express your secret sin you would be keeping stress and tension locked up inside you, but if you express it, the stress and tension will be relieved. Another reason behind the veil might be sorrow. Deep, dark sorrow for someone or yourself might be expressed and shown with the help of a black veil.
By wearing the black veil for eternity, you are exhibiting great love and sorrow for someone or yourself. If the black veil was removed, the sorrow and love would be dead. This might be how Reverend Hooper expressed the veil. Father Hooper might have also used the veil as a friend and a device to test Elizabeth's love for him. The black veil might have given Mr. Hooper friendship if he was lonely and without a mate. He could test Elizabeth to see if an object would come between them