What does John 10:6 mean?

Jesus has just made the first of three analogies related to shepherding found in this chapter. These are spoken to the hostile religious leaders who dispute Jesus' giving sight to a man born blind (John 9). In this metaphor, Jesus indicated that those who do not listen to His voice are like sheep belonging to a different shepherd. Those who do listen are those who belong to Him.

In that era, sheep would be kept in large pens holding several flocks. These structures had a single narrow opening, and this is where all of the animals would come and go. The gatekeeper would ensure that only legitimate shepherds could access the sheep. When a shepherd needed to bring out his animals, all he had to do was call to them. Since these animals lived their entire lives around that one person, they would respond only to that voice.

By analogy, Jesus is implying that the reason these religious critics don't listen to His words is because they belong to another master. In an earlier conversation, Jesus directly told men like these that they were children of the Devil (John 8:42–47). As such, they'd never choose to respond to God, but would recoil, instead.

Of course, as those not inclined to listen to Jesus in the first place, these men fail to grasp the point being made. Instead, as seen in later verses, they will try to write Him off as a babbling maniac (John 10:19-21).