Simon Peter was becoming a powerful man in Christ, so Satan himself wished to get him into his power so he could destroy him. "And the Lord said, Simon, Simon, behold, Satan has desired to have you, that he may sift you as wheat.” But I have prayed for you, that your faith fail not: and when you are converted, strengthen your brethren. (Luke 22:31/32)
The Devil already has the entire world population of sinners captive to his power, but Peter the powerful Apostle came into the Light of Christ supernaturally and was a threat to the works of the Devil, "in whom the god of this world has blinded the minds of the unbelieving, that the light of the gospel of the glory of Christ, who is the image of God, should not dawn upon them. (2 Corinthians 4:4)
Saint Paul wrote regarding the Apostles; that God "delivered us from the power of darkness, and has translated us into the kingdom of his dear Son:" (Colossians 1:13) The Apostles were a threat to the Devil. They walked in kingdom power.
So, when Satan went in with the Sons of God to the throne room of the LORD, he petitioned God for permission to sift Peter as wheat, but the Lord Jesus Christ interceded for him.
The whole world is in conflict between good and evil, God and Satan. That is why the Lord said he would rather you would be hot or cold rather than lukewarm. If you are lukewarm, he has promised to spit you out. Think about it. The Lord interceded for Peter. What do you think the Lord would have done were Peter lukewarm?
We don't fight spiritual warfare alone. If God be for you, who can be against you?