6 Jesus used this illustration, but they did not understand the things which He spoke to them.
John closed this illustration with a note of explanation to show that the Pharisees did not grasp the significance of what Jesus said. They were the false teachers that genuine believers will not follow.
6 Jesus used this illustration [image, figure],
The word “illustration” is the word for figure of speech. An allegory (extended metaphor) is an implied comparison drawn from everyday life that illustrates a biblical principle.
but they did not understand the things which He spoke to them.
The Pharisees did not grasp the meaning of the allegory. The point of this figure was that those who genuinely believe in Jesus will follow Him.
Jesus theologically indicts those who mislead others.
The point of this parable is to show how a shepherd forms his flock. Those who respond to the call of the Shepherd are genuine believers. The proper response of sheep is to follow. Most people never grasp this lesson from Jesus and eternal life.
Jesus spoke in a parable to hide His meaning from fakers and to expose truth to genuine believers (Mt 13:10-16).