Aside from the fact that these three questions parallel the triple denial of Jesus by Peter, what else might they signify? To me they show that although Peter failed Jesus miserably in his hour of need, God's call on Peter's life still remains. Peter's failure did not negate the call of God on his life. God has not given up on Peter.
Jesus then says to Peter here at the end of the gospel the same thing he said at the beginning, "Follow me." But now Peter knows what "follow me" entails - persecution, being an outcast, danger, trials and death.
Peter had already passed one small test since his denial and Jesus' resurrection: he fished on the other side of the boat when Jesus told him to. Now Jesus gives him a much bigger task: follow me and feed my sheep.
For reflection: My failure does not negate the call of God on my life.
Let us pray. Lord, I may not always be successful, but I want to be faithful. Don't let my failures keep me from trying to what you call me to do.