The disciples would be left behind in a hostile world when Jesus went back to heaven.  It was all part of the plan.  Instead of taking them with Him, Jesus deliberately put the disciples into ‘enemy territory’ so that they could tell the world about Him.  Jesus could not pray that the Father would take them out of the world – they were there for His divine reason to continue the work of Jesus.  As more people believed in Jesus, so the church would grow.  However, Jesus was fully aware of the dangers and so prayed that Father God would protect them from the Evil One.
 
The disciples were no longer under the control of Satan, because they were following Jesus: but Satan would try to destroy them or disable their ministry if he could.  So God’s protection was essential.  Also, Jesus wanted His men to be full of truth in order to combat the devil’s lies.  So, He prayed that they would become special and close to God – desiring to know the truth and to live differently because they belonged to Jesus.  In that way, the apostles were sent into the world with the same sense of commission that Jesus had received from His Father.

How would the apostles stay close to the Lord?  Only by continually refreshing and washing themselves in His Word – to nourish their spirits with His truth and show them their sin of which to repent (John 13:6-11; John 15:3).  Without God’s Word we cannot know what is right or wrong; but when we know what is right and repent of what is wrong then we are protected from Satan’s lies.
 
It is the same for us.  God’s Word needs to set the agenda for our thinking and daily purpose.  Unless we live in the truth, we will inevitably succumb to the devil’s lies.  As we allow His Word to work in us, we will become God’s holy (sanctified/set-apart) people; and then we will have competence and confidence to share His Word with others.  It is a dangerous world with many hidden spiritual traps, but we can be sure that Father God will protect us as long as we stay in tune with His Word.