What was the subject of Minister Hooper's first sermon while wearing the veil?

In Hawthorne's "The Minister's Black Veil," Reverend Hooper's first sermon concerns secret sin. The townspeople are all rather taken aback by both the veil and the darker, gloomier tone of the sermon.

Of course, following the sermon is the funeral of a young woman from the town. The funeral, the veil, and the sermon are not mere coincidences; they are all inter-connected, leading many of the townspeople to believe that Reverend Hooper and the young woman were romantically involved.

Reverend Hooper continues to wear the black veil for the rest of his own life, refusing to remove it even on his own deathbed.