Matthew 16:15-17
He saith unto them, But whom say ye that I am?
And Simon Peter answered and said, Thou art the Christ, the Son of the living God.
And Jesus answered and said unto him, Blessed art thou, Simon Bar-jona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven.

Luke 22:32
But I have prayed for thee, that thy faith fail not: and when thou art converted, strengthen thy brethren.

COMMENTARY

The above passages represent Jesus addressing Simon Peter at two different points in time: one in the middle of his ministry, and the other immediately before Jesus’s atoning sacrifice and crucifixion.
The significance of these two scriptures laid side-by-side I cannot claim to have discovered myself. Rather I will present two excerpts from Elder Dallin H. Oaks’ October 2000 address entitled The Challenge to Become:

1)

…And Jesus answered and said unto him, Blessed art thou, Simon Bar-jona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven

Peter had a testimony. He knew that Jesus was the Christ, the promised Messiah, and he declared it. To testify is to know and to declare.

2)

I have prayed for thee, that thy faith fail not: and when thou art converted, strengthen thy brethren.

In order to strengthen his brethren—to nourish and lead the flock of God—this man who had followed Jesus for three years, who had been given the authority of the holy apostleship, who had been a valiant teacher and testifier of the Christian gospel, and whose testimony had caused the Master to declare him blessed still had to be “converted.”

Jesus’ challenge shows that the conversion He required for those who would enter the kingdom of heaven was far more than just being converted to testify to the truthfulness of the gospel. To testify is to know and to declare. The gospel challenges us to be “converted,” which requires us to do and to become. If any of us relies solely upon our knowledge and testimony of the gospel, we are in the same position as the blessed but still unfinished Apostles whom Jesus challenged to be “converted.”