The shepherd's job is to lead the sheep to good pasture and to protect them.  Jesus is the Shepherd and He guides everyone who listens to His words and obeys them (Psalm 23:1-6).  He leads them to live a spiritually healthy life, called 'eternal life' - which starts when we are born again and continues through death into an eternity of provision and service.  While He leads us, nobody (person, angel or demon) has any authority to capture us, and take us away from Jesus or Father God (Romans 8:38-39).
 
Neither the devil nor his demons can pull people out of God's kingdom.  They are safe in Jesus’ hand and Father God’s hand.  It is also true that Jesus will not throw anyone out of His kingdom (John 6:37-40).  All those who come to Jesus are kept safe by Him.  We may sometimes feel that our grasp on the Lord is weak, but His grip on us never changes and always keeps us safe (Psalm 139:7-10).  

However, if we love Him who has given Himself for us (Ephesians 5:1-2) we will want to keep in step with Him (Galatians 5:24-26).  Because of our love relationship with Him, we should want to continue to follow Him and obey Him.   The Bible gives no comfort to those who persistently rebel,  and urges believers to continue trusting Jesus (Colossians 1:22-23, Hebrews 3:14).  So, although there is a constant challenge to stay close to the Shepherd, we should not be frightened that Satan can ever drag us away from God’s love, or that He will want to throw us out of His kingdom.
 
Yes, Satan may tempt us, and often does - and we may give in to some temptations - but the sheep who is truly in Jesus' flock will realise that there is no other shepherd who is strong enough to deliver, and merciful enough to forgive.  1 Corinthians 10:13 says, "No temptation has overtaken you except what is common to mankind. And God is faithful; he will not let you be tempted beyond what you can bear. But when you are tempted, he will also provide a way out so that you can endure it."  The guarantee that Jesus gave is matched by the guarantee of God the Father - that no-one can snatch us out of God's hand.  So let us rejoice in our security, repent of wandering away, and return to our Shepherd in repentance and faith.