Peter had embraced the message of Jesus. He gave up career and family to follow Jesus.  When other followers walked away, Peter pointed out that no one else had the words of eternal life.  However, even that level of belief was not sufficient to carry him through Jesus' arrest and trial.  Peter denied knowing Jesus.  However, after being filled with the Holy Spirit, Peter boldly proclaimed Jesus to the same people before whom he had previously denied him.  He had been filled with the Spirit.  His existence was no longer about himself.  It was about Jesus