What is the meaning of this quote from "The Minister's Black Veil"?

“When the friend shows his inmost heart to his friend; the lover to his best-beloved; when man does not vainly shrink from the eye of his Creator, loathsomely treasuring up the secret of his sin; then deem me a monster, for the symbol beneath which I have lived, and die! I look around me, and, lo! on every visage a black veil!”