Strange though it may seem, Satan has to apply to God to do his wicked work (Job 1:6-12).  The Evil One had already been given permission to enter into Judas (Luke 22:3) – he had Jesus’ permission but make no mistake, Judas was intent on betraying Jesus and was fully responsible for that desire and behaviour.  Then, Satan wanted to invade Simon Peter's life, but Jesus intervened.  A test of Peter's loyalty would still be allowed, and he failed that test (Luke 22:54-61), but Satan was denied permission to rip his faith into shreds and prevent him from repenting and being restored to fellowship and usefulness.
 
Jesus had prayed for Peter.  The Father and the Son together agreed that Satan should not have ultimate liberty with the apostle's life.  He had a job to do to strengthen the Church - a fresh commission which Jesus would personally give him after the resurrection (John 21:15-19).  But, before he could be recommissioned, he had to learn the grace of repentance.  That was the big difference between the remorse of Judas and the penitence of Peter: one led the dishonest treasurer to destruction (Matthew 27:1-10), the other brought the arrogant fisherman to his knees (Luke 22:62).  Both were helpless sinners, but Simon Peter's heart was soft towards Jesus, and the Master prayed for Him.
 
What a difference that advocacy made.  And it is wonderful to know that Jesus is still praying for those who belong to Him.  He approaches Father God as a defending attorney, claiming His blood as the sacrifice for our sins so that we might be declared righteous (1 John 2:1-2).  Often, when we don't know how to pray for ourselves, the Holy Spirit will pray for us because we belong to God (Romans 8:26-27).  

Although we are under an obligation to love and serve our God wholeheartedly, we cannot do so unless He helps us.  Yes, we must fight against the world, the flesh and the devil; but unless the Lord helps us, we will certainly fail.  In the same way, we should be praying for God's will to be done.  But sometimes it is so difficult to pray, and we need the Bible’s assurance that the Holy Spirit presents our heart desires before the throne of heaven.  This is no excuse for weak-hearted discipleship - but the simple reality is that, however strong we are, we need His strength if we are to do His will and stay within the orbit of His grace.