These words were supposedly spoken by Moroni to Joseph Smithin 1823. He was quoting from Malachi 4:5, which says nothing about the priesthood.
This misquote of Malachi 4:6 seems to say that God won't destroy everyone on the great and dreadful day of the Lord. But that the day will come shortly after the priesthood is revealed.
Well the priesthood was supposedly revealed, and nothing happened for 190+ years.