What does John 10:4 mean?

In Jesus' era, several separate flocks of sheep would be housed in a single sheep pen. These structures were walled off to prevent other animals from getting in. They also featured a single, narrow opening. The gatekeeper of the pen would only allow approved shepherds in or out. The only reason for someone to climb over the walls would be theft.

To get a particular flock back out of the pen, a shepherd could simply call them. The nature of shepherding means those animals were constantly being spoken to by that one man. In response to his voice—and his voice alone—they would come to the doorway to be let out by the gatekeeper.

Jesus is following his confrontation with religious leaders in chapter 9, where He gave sight to a man born blind. The metaphor He uses here echoes what Jesus told His critics in John 8:42–47. Namely, that they did not listen to Jesus because they were not "His." Those who belong to God recognize the voice of God. But, like sheep from a foreign flock, those who belong to the Devil don't respond when called by Christ.

Jesus will follow this analogy with two more analogies that flesh out the idea that Jesus is the one and only means of salvation, and that those who are part of God's kingdom will recognize no other except Him.