Today's Favorite Verse: Doctrine & Covenants 13:1
"Upon you my fellow servants, in the name of Messiah I confer the Priesthood of Aaron, which holds the keys of the ministering of angels, and of the gospel of repentance, and of baptism by immersion for the remission of sins; and this shall never be taken again from the earth, until the sons of Levi do offer again an offering unto the Lord in righteousness."
On May 15, 1829 an angel appeared to Joseph Smith and Oliver Cowdery, and called himself John. The very person called John the Baptist in the New Testament. He was sent to earth to restore the keys to the Aaronic Priesthood for which he held. He gave those priesthood keys to Joseph and Oliver and instructed them in the ordinance of baptism. This priesthood authority would never again be taken from the earth, until the sons of Levi do offer again an offering unto the Lord in righteousness.
I'm not really sure what happens to these keys of authority when that event happens. Interestingly there is a sect of Jews making preparation for such an offering once again. I am not sure if that is what this scriptures means. I do know that since this is the dispensation of the fullness of time, all things need to be restored before the Savior's second coming. Even the sacred offerings by the sons of Levi, in righteousness. That is why the law of Sarah, or polygamy was restored for a brief time period too. You cannot have a fullness if all ordinances and laws are not restored at their proper time.