There is a difference between receiving a testimony of truth and being truly converted. For instance, the great Apostle Peter bore his witness to the Savior that he knew that Jesus was the Son of God.
“[Jesus] 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” (Matthew 16:15–17).
And yet later, in His injunction to Peter, the Lord gave him and us a guide to become truly converted and to extend that conversion for a lifetime. Jesus said it this way: “When thou art converted, strengthen thy brethren” (Luke 22:32).
Jesus taught Peter that there was still a great change that must go beyond having a testimony to being able to think, feel, and act as truly converted disciples of Jesus Christ. That is the mighty change we all seek. Once we obtain it, we need that change to continue until the end of our mortal probation (see Alma 5:13–14).