Joseph Smith - History 1

After Oliver Cowdery began assisting the translation of the Book of Mormon as a scribe for the Prophet, the Prophet Joseph Smith records that -

"...we on a certain day went into the woods to pray and inquire of the Lord respecting baptism for the remission of sins, that we found mentioned in the translation of the plates."  (Pearl of Great Price | JS-History 1:68)

And thus -

"...While we were thus employed, praying and calling upon the Lord, a messenger from heaven descended in a cloud of light, and having laid his hands upon us, he ordained us, saying:
69 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."  (Pearl of Great Price | JS-History 1:68 - 69) (See D&C 13)

After conferring the Priesthood of Aaron upon both brethren -

"He said this Aaronic Priesthood had not the power of laying on hands for the gift of the Holy Ghost, but that this should be conferred on us hereafter; and he commanded us to go and be baptized, and gave us directions that I should baptize Oliver Cowdery, and that afterwards he should baptize me.
71 Accordingly we went and were baptized. I baptized him first, and afterwards he baptized me—after which I laid my hands upon his head and ordained him to the Aaronic Priesthood, and afterwards he laid his hands on me and ordained me to the same Priesthood—for so we were commanded."  (Pearl of Great Price | JS-History 1:70 - 71)

It appears that authority by receiving the priesthood was essential to act in the name of God.  After having been baptized constituted a change of status which upon they were ordained to the priesthood or in other words, received an essential ordinance. 

The Prophet adds -

"The messenger who visited us on this occasion and conferred this Priesthood upon us, said that his name was John, the same that is called John the Baptist in the New Testament, and that he acted under the direction of Peter, James and John, who held the keys of the Priesthood of Melchizedek, which Priesthood, he said, would in due time be conferred on us..."  (Pearl of Great Price | JS-History 1:72)

As the messenger conferred the priesthood, he used the word "until" in "until the sons of Levi".  The word "until" may have had a slight different meaning than in our present day.  It is interesting that in Oliver's account, the messenger used the word "that".  We find similar references in scripture where the Savior said that -

"...he shall purify the sons of Levi, and purge them as gold and silver, that they may offer unto the Lord an offering in righteousness."  (Book of Mormon | 3 Nephi 24:3)

As well as -

"...he shall purify the sons of Levi, and purge them as gold and silver, that they may offer unto the Lord an offering in righteousness. Let us, therefore, as a church and a people, and as Latter-day Saints, offer unto the Lord an offering in righteousness..."  (Doctrine and Covenants | Section 128:24)

This would suggest the this priesthood then would never be taken from the earth.