When sheep wander, they are at risk of being stolen.  Grazing for most of the daylight hours and covering as much ground as is needed to supply the food, sheep can roam a long way from the flock and be separated, out of sight of the shepherd.  But paradoxically, the risk increases when all the animals are together in the sheep pen because thieves have an easier target.  In this chapter, Jesus introduces Himself as the Good Shepherd (John 10:11): but He starts by speaking about false shepherds who were really thieves. They had no right to put sheep under their arms and carry them away; they have no care for the sheep, only what they can get out of them (Jeremiah 23:1).
 
Jesus identified the Pharisees, who ruled religious life at that time, as sheep stealers.  Although they claimed to guard God's people, and feed them with truth, their real interest was to advance themselves (Matthew 23:13-15).  They enjoyed the honour which people gave them; and their proud hearts were pleased when people looked up to them - giving them the power to control the worshippers.  It was like being more dangerous than hungry wolves to sheep, because they lived in the sheepfold – controlling the places where people came to worship – although they were selfish and malignant hypocrites (Ezekiel 22:27).  

Those sheep stealers refused to honour Jesus; indeed, they hated Him (Luke 19:14).  Instead of being glad that God had sent His Son into the world to be the atoning sacrifice for their sins, they bitterly envied the way the people responded to Him (Mark 15:10), resented His power to meet so many human needs and resented the divine authority in His teaching (Matthew 7:29).  They saw that people gladly came to Him and received selfless love from Him.
 
Religion which does not allow Jesus Christ to be the Shepherd, however moral and virtuous it may appear to be, will always provide an opportunity for so-called 'spiritual people' to steal the hearts of God's people.  Instead of leading them to Christ so that they may find Father God, they offer a different way to God.  Spiritually hungry people are easily trapped by false prophets; and those who are desperate for an encounter with the living God can easily be seduced with offers of new and satisfying experiences.  Sometimes these sheep stealers even disguise themselves as spiritually eager people to get inside the church and be accepted … before they start networking amongst the vulnerable to lead them astray.  But as Jesus said, "Watch out for false prophets. They come to you in sheep's clothing, but inwardly they are ferocious wolves." (Matthew 7:15)