“Simon, Simon, behold, Satan has demanded permission to sift you like wheat;
   but I have prayed for you, that your faith may not fail; and you, when once you have turned again, strengthen your brothers.” - Luke 22:31-32

 Notice it doesn't say if, it says when.

 It's the Lord's Supper, Jesus disciples are eating with Him including Peter. They are all very acquainted with each other having spent years thus far in the apostleship together partaking in the ministry and witnessing many miracles. They all share in the first communion with the Lord, followed up by a hymn. Then they part from there together to the Mount of Olives. (Matt. 26:26-30). 

   Then Jesus said to them, "You will all fall away because of Me this night, for it is written, 'I WILL STRIKE DOWN THE SHEPHERD, AND THE SHEEP OF THE FLOCK SHALL BE SCATTERED.' - Matthew 26:31

   Peter having never witnessed Jesus tell a lie, having seen everything come true that Jesus had said to be thus far, does he heed Jesus words?

   But Peter said to Him, "Even though all may fall away because of You, I will never fall away." - Matthew 26:33

   Hmm, perhaps if Jesus reiterates his point to Peter by giving him additional details.

   Jesus said to him, "Truly I say to you that this very night, before a rooster crows, you will deny Me three times."

   Yes yes, that should do it, now Peter will understand.

   Peter said to Him, "Even if I have to die with You, I will not deny You." All the disciples said the same thing too. - Matthew 26:35

   Now I assure you Peter's heart here is gold, his love is genuine, and his zeal for the Lord goes unquestioned. But does he take to heart Jesus word? Well, lets just say this isn't the only time he's been stubborn. See Acts 10:9 - 17.

   Now back to our story. Some time has gone by, Jesus is arrested, and the events unfold as Jesus prophesied. Peter in three difference instances denies Jesus. (Matt. 26:69-75). But at the end of the third denial a rooster crows which was an anchor in Peter's mind to what Jesus had told Him. When the rooster crowed it brought everything Jesus had said to memory, and now the words spoken by the Lord strike home, now they penetrate to Peter's heart.

   And Peter remembered the word which Jesus had said, "Before a rooster crows, you will deny Me three times." And he went out and wept bitterly. - Matthew 26:75

   Perhaps you have read this like I and know all to well what it is to weep bitterly. Angrily crying with hurt that strikes the deepest parts of our inner being. Peter understands, and Jesus understands. (Luke 22:28, John 11:35, Heb. 2:18, 4:15, Isa. Ch. 53).

   Before I continue I want you to know this, God is not caught off guard by your failure. He is not surprised at the decisions you make. You have the freedom to choose, but God already knows that which you will pick. He knows this about you, and as we read here, He knew this about Peter. Knowing Peter would fail Him, did He still not save him? Most assuredly He did. Knowing you would fail him, did He not still die on the cross for you? Most assuredly He did. You see when God called you, He already knew the full package that is you. He was fully aware of all the failures that came with you, past, present, and future. And with Christ's finish work on the cross, (John 19:30) He was free to fully accept you as His child just the way you are, and to justly lavish His unconditional grace upon you (Isa. 30:18).

   What happened with Peter, which also happens with us is God's plan doesn't line up with our plan, or rather, our plan fails to line up with God's plan. When our circumstances do not coincide with our understanding of how we believe they should be, it feels "as though some strange thing were happening" (1 Pet. 4:12), and thus doubts arise. In Peter's case, he had something that needed sifting, and God was going to orchestrate this trial to work on that very thing. Luke records an aspect of this story that sheds light on this orchestration. This takes place just before Jesus informs Peter about how he would deny Him three times.

   "Simon, Simon, behold, Satan has demanded permission to sift you like wheat; but I have prayed for you, that your faith may not fail; and you, when once you have turned again, strengthen your brothers." - Luke 22:31-32

   First let me point out that Jesus doesn't say if, He says when. Jesus never planned on setting Peter up for ruin though I'm confident Peter felt that way. Jesus was faithful in sustaining Him. (1 Thess. 5:24). Next I want to point out the prayer Jesus petitioned on Peter's behalf; that his faith would not fail! That said, I think it's safe to say his faith is going to encounter some hardship. It's interesting that during this agonizing trial Peter was about to go through, the petition the Lord would lift up on Peter's behalf is that his faith would not fail. Why not pray for Peter not to deny Him, or have the opportunity to deny Him removed and avoid this hardship altogether, because that would defeat the purpose and fruit this trial would produce. Next look how Satan, who intends only harm (John 10:10), is used as a tool to bring about the purpose that God has set forth in Peters life; that is the process of sifting. Jesus informs Peter of Satan's request to sift him like wheat. The process of wheat sifting consists of separating the undesired chaff from the edible grain of wheat. Because the two are so closely joined, it can be a long, painful and tedious process separating them but the end result is one that is a fruitful ingredient useful for a variety of dishes.

   You see Peter had to be sifted of something. He had to be refined, having the bad separated from the good. Was this an easy process to undergo? Absolutely not. Was it a beneficial process? Most assuredly. If you feel you have failed in this trial, take courage, so did Peter. (Matt. 26:75). But know that God has every hair on your head numbered (Matt. 10:30), and this trial you're going through has not escaped His notice. In fact, it has been filtered by the hands of the God who is your ally.

   And we know that God causes all things to work together for good to those who love God, to those who are called according to His purpose. For those whom He foreknew, He also predestined to become conformed to the image of His Son, so that He would be the firstborn among many brethren; and these whom He predestined, He also called; and these whom He called, He also justified; and these whom He justified, He also glorified. What then shall we say to these things? If God is for us, who is against us? - Romans 8:28-31

   I've seen when engineers and contractors build a bridge, one of the first things they do upon completion is find one or more heavy pieces of machinery used to build the bridge and park it right in the middle. They often leave it there for several days with the purpose of testing the bridge. This isn't to bring about destruction of their long painstakingly hard work, but rather to identify any weak points that may need to be fixed before commissioning the bridge for public use. They do this to find out how strong the bridge is, and to identify and correct any weaknesses that could later turn into a major disaster if not corrected.

   Understand that God is for you in this trial, much like the bridge analogy above, James applies a similar model to our lives;

   Consider it all joy, my brethren, when you encounter various trials, knowing that the testing of your faith produces endurance. And let endurance have its perfect result, so that you may be perfect and complete, lacking in nothing. - James 1:2-4

   Consider it joy means count it as a blessing, not necessarily feel it as a blessing, at least not right now.

   After you have suffered for a little while, the God of all grace, who called you to His eternal glory in Christ, will Himself perfect, confirm, strengthen and establish you.- 1 Peter 5:10