Peter said unto him, Lord, why cannot I follow thee now? I will lay down my life for thy sake.  Jesus answered him, Wilt thou lay down thy life for my sake? Verily, verily, I say unto thee, The cock shall not crow, till thou hast denied me thrice. (John 13:37-38)
 So when they had dined, Jesus saith to Simon Peter, Simon, son of Jonas, lovest (agapâis)thou me more than these? He saith unto him, Yea, Lord; thou knowest that I love (phileô)thee. He saith unto him, Feed my lambs.  He saith to him again the second time, Simon, son of Jonas, lovest (agapâis) thou me? He saith unto him, Yea, Lord; thou knowest that I love (phileô)thee. He saith unto him, Feed my sheep.  He saith unto him the third time, Simon, son of Jonas, lovest (phileô)thou me? Peter was grieved because he said unto him the third time, Lovest (phileô)thou me? And he said unto him, Lord, thou knowest all things; thou knowest that I love (phileô)thee. Jesus saith unto him, Feed my sheep.  Verily, verily, I say unto thee, When thou wast young, thou girdedst thyself, and walkedst whither thou wouldest: but when thou shalt be old, thou shalt stretch forth thy hands, and another shall gird thee, and carry thee whither thou wouldest not.  This spake he, signifying by what death he should glorify God. And when he had spoken this, he saith unto him, Follow me. (John 21:15-19)
I believe that before Peters re-installment he must have been feeling very mixed up emotionally. He would have been feeling very low and would have repented deeply for the three denials, whilst also very elated with excitement and wonder. Jesus is alive! When Peter denied Christ leaving Christ to face His trial on His own, not only was it a denial but it resulted in sin, because his denial was a lie. Peter did know Jesus… yet said he did not know Him.
However, this sin was shortly after paid for on the cross – by the blood of Jesus. Can you imagine, even though Peter must have been thinking “I added to Christs suffering due to that lie” and “If I had kept my promise and died for you then I too should have been on a cross – next to you my King.” However the Lord had a different plan for Peter, and the Lord did what He always does, He turned what was bad into Good – because Peter by being alive becomes one of the key figures in establishing His Church, Peter became a fisher of Men, Peter remains alive and his sins washed clean by the very blood of the Lord that He had just denied even knowing! God shows Grace and Mercy for Peter.
So the Lord speaks with Peter and seeks to re-instate him as an Apostle to build His Church. Peter clearly has trouble in responding to our Lord. Why? It is because of the past that he has not yet learned to let go. He does not yet understand in his heart that by Christ now being back from the dead, and the fact that Peter believes in Him resurrected – that this makes him a Christian! and this means all of Peters sins are now erased as if they did not happen… therefore Christ does not focus on the Simon with denials but the focus is on “Peter the Rock.” You see Simon is the old man and Peter is to be the new Man, the changed Man whom will soon tell God he loves Him three times to make up for the three denials.
So Christ asks Peter “Do you Love me” using the word ‘agapais’ for unconditional sacrificial love. However Peter was doubting due to the past – he felt unable to reply with the stronger word for love that was agapais. He replied with ‘phileo’ meaning “I love you with affection – as a friend” so Peter was not really answering. Peter after his statement in John 13:37-38 said he was ready to die for the Lord yet he went on to deny Him three times. (and Jesus once said in John 15:13 “Greater love has no one than this, than to lay down one’s life for his friends.”) So now he was doubting himself and unable to say ‘agapais’ and chose to use the lesser word ‘phileo’ yet no doubt Peter also realised how Jesus had just died on the cross for the entire world with both ‘agapais’ and ‘Phileo’ for all of us – Jesus lived up to the meaning of the term ‘agapais’ and ‘Phileo’, something Peter was unable to previously do.
Now we notice by the third time Jesus asks Peter Jesus resorts to the lesser word of ‘phileo’. This seems to upset Peter and I don’t think just because it reminded Peter of his three denials but also because Jesus changed his question to match Peters own words, thus acknowledging that Peter was doubting and not really answering. Now Peter once again perhaps felt he had denied Christ because now Jesus had also lessened His question – a bit like psychology – you know how if you talk with someone you can sometimes mimic that persons own character? and so Peter lost his chance to say “Yes Lord I really do agapais you”
BUT notice –
Jesus then tells Peter how he will die…. why would He do this? He also states that Peter shall glorify God. Here I think Jesus was comforting Peter to remove his doubts by letting Peter know, by saying to Peter (in a sense) “Peter you will live to a good old age, also you said previously you will die for Me, and do not worry, do not doubt Peter – because you do agapais Me. You will surely die for Me at an old age and never deny Me, you will glorify Me. So do not live your life fearing and in doubt – I know all things just as you have said! I know you agapais Me.”
Peter had just said in John 21:17 “And he said unto him, Lord, thou knowest all things” as Peter had witnessed fully by Jesus prophesying the three denials. Peter trusted the Lord.
By telling Peter all this, Peter could live his life serving the Lord knowing that he will live to a good old age without wondering if he will deny the Lord again. Legend has it that Peter later died on a cross upside down – crucified. So if this is true then it means Peter did in the end take his place on the cross just as he would have done many years before if he had kept his promise.
Jesus got to the heart of the matter. It is about the condition of our hearts – examine our hearts and mind. Simon was the old man – and Peter is the new man. However Peter would have to keep on putting this new man on daily by resting in the Lord and following Him – just as we all need to do.
Ephesians 4:21-24 – 21 If so be that ye have heard him, and have been taught by him, as the truth is in Jesus: 22 That ye put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts; 23 And be renewed in the spirit of your mind; 24 And that ye put on the new man, which after God is created in righteousness and true holiness.