This is a frightening passage, but it also holds great comfort for Christ's disciple. Satan attacks God by attacking God's people. Satan releases his fury and power against God's people in an attempt to hurt God. This attack is called "sifting" in the text. The word, "sift", contains the ideas of pain, struggle, and hardship in it. How terrible it is that some preachers tell people that if they are "right with God", then they will not struggle at all. The Christian life is inundated with struggle, but this is not bad. This shows two things: (1) Christians have spiritual life, and (2) Satan hates them for it.
But Jesus told Peter that He was praying for Peter. And Jesus is praying for us. One of the most encouraging parts of the gospel is the intercessory, mediatorial ministry of Jesus Christ. He prays continually for each of His people by name and need at the throne of the Father. This has often given me comfort and strength to keep going - Christ is praying for me. He is praying for us concerning our justification and our faith. Jesus is praying that our faith will not fail, and our faith will not fail, because Jesus is praying for this very thing.
And Jesus also said that Peter would need to repent ("turn again"). This implies that there will be times when we will wither in the heat of spiritual battle. Our strength is not sufficient, and sometimes the Lord allows us to fall. But we will not utterly fall; we cannot utterly fail. A Christian's fall is not fatal; the Lord will always bring us back. He Himself will see to this. He will not allow us to absolutely and completely fall. He will always bring us back. And when we are renewed and restored, then we must help out our brothers and sisters in Christ, as the text says. We are not meant to fight the battles alone, and we must seek to help our spiritual family with their struggles in battle.
Several implications and applications come to mind as we ponder what Jesus said:
1. Christian, expect to be attacked; this is normal and natural in this world of sin.
2. Don't be overwhelmed by spiritual attack. Keep fighting, and do not lose hope.
3. The Lord is with us everywhere all the time; we are never forsaken.
4. There will be set backs, but we must always come back to the Lord.
5. Spiritual battle has both individual aspects and community aspects as well. Stick together as Christians.