Come Follow Scripture - D&C Section 2 - the 3 orders of the Priesthood

D&C Section 2 - The angel Moroni appeared to Joseph Smith and told him that Elijah would come and "I will reveal unto you the priesthood by the hand of Elijah the prophet before the coming of the great and dreadful day of the Lord...". What is this priesthood? We know that Peter, James, and John brought back the keys of the Melchizedek Priesthood to Joseph Smith, and John the Baptist brought back the keys of the Aaronic priesthood, so what is this priesthood that Elijah is referring to? We will delve into this mystery with a little dash of history as we go. We sill also refer to the 3 orders of the priesthood as Joseph Smith taught and link all of this to the temples that are being constructed in the latter days.