D&C 7

As the Prophet Joseph Smith received a revelation of that recorded by John on parchment, the Lord said to Peter -

"If I will that he tarry till I come, what is that to thee? For he desired of me that he might bring souls unto me, but thou desiredst that thou mightest speedily come unto me in my kingdom.
5 I say unto thee, Peter, this was a good desire; but my beloved has desired that he might do more, or a greater work yet among men than what he has before done."  (Doctrine and Covenants  Section 7:4 - 5)

I think "greater work" was defined by "do more" in this life.  Peter's work would continue on the other side of the veil.  But what caught my attention was the instruction to Peter -

"...I will make thee to minister for him and for thy brother James; and unto you three I will give this power and the keys of this ministry until I come."  (Doctrine and Covenants  Section 7:7)

I interpet that to mean the these three holds the keys of this ministry or the Church and is senior and presides over all other Church presidencies since the ministry of the Savior.  Is it any wonder that these three conferred the keys of the Melchizedek priesthood to the Prophet Joseph Smith and Oliver Cowdery.  We see their leadership in much of our holy teachings.