Read: 1 Corinthians 15:1-11
For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures, and that he appeared to Cephas, then to the twelve. (1 Corinthians 15:3-5 ESV)
I can't help it. When I consider death I think of the finality of it. It just sounds like an ending. And, in spite of my belief about the afterlife, anytime someone I am close to dies it feels like a forced goodbye.
I think Peter must have felt much the same way about Jesus. The resurrection wasn't something to they were counting on. No one had done it before. And even though Jesus told them exactly what would happen! it seems like they largely missed the point.
So when Jesus began to appear to his disciples I can't imagine how they must have felt. It would have been like seeing something you believed to be impossible happen right before your eyes. Like seeing a fallen leaf fall up or a man flying under his own power.
Death feels certain. And life after death unknown. We believe, and we hope we know, but we don't know for certain. Peter had his conviction steeled the day the risen Son of God appeared to him. The man he loved demonstrate the reality of his deity by returning to life. Everything changed for him he day that Peter saw Jesus.