This prophecy can be read in two ways. The first is that “a man” is literally a single man. That would clearly mean Joseph Smith would be the one to bring the record to light to provide its teachings. He would be persecuted, but Jehovah would protect him to be able to deliver the message. Of course, that happened.
The second reading is that “a man” is generic. It could apply to all of us who, believing, share our beliefs and attempt to spread the gospel. We too may be preserved in our efforts.
Of course, Joseph’s martyrdom declares that the divine protection covers a specific mission, and does not assure a life free from harm, difficulties, and eventually death.