His great love for the Savior began before Jesus Christ's public ministry, for he was a disciple of John the Baptist.
"And the Lord said unto me: John, my beloved, what desirest thou? For if you shall ask what you will, it shall be granted unto you.
And I said unto him: Lord, give unto me power over death, that I may live and bring souls unto thee.
And the Lord said unto me: Verily, verily, I say unto thee, because thou desirest this thou shalt tarry until I come in my glory, and shalt prophesy before nations, kindreds, tongues and people.
And for this cause the Lord said unto 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.
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.
Yea, he has undertaken a greater work; therefore I will make him as flaming fire and a ministering angel; he shall minister for those who shall be heirs of salvation who dwell on the earth." (D&C 7:1-6)