"'Most assuredly, I say to you, he who does not enter the sheepfold by the door, but climbs up some other way, the same is a thief and a robber. But he who enters by the door is the shepherd of the sheep. To him the doorkeeper opens, and the sheep hear his voice; and he calls his own sheep by name and leads them out. And when he brings out his own sheep, he goes before them; and the sheep follow him, for they know his voice. Yet they will by no means follow a stranger, but will flee from him, for they do not know the voice of strangers.' Jesus used this illustration, but they did not understand the things which He spoke to them."
This appears to be a continuation of the previous context in which Jesus had declared the spiritual blindness of the Pharisees. Jesus used this illustration to further prove that point (cf. John 10:6) as well as to establish himself as the door and good shepherd of the sheep. He was not a thief, robber, or hireling (cf. 10:7-18).
Jesus begins by stating that one who enters the fold (i.e., a roofless enclosure used to protect the sheep) in some way other than through the door is there to do harm. Only the true shepherd enters into the fold through the door. Jesus was (and is) the true shepherd (cf. 10:11; Psa. 23; Ezek. 34:31). He always has the best interests of the sheep in mind. The Jewish religious leaders were false shepherds (cf. Ezek. 34:1-6) who intended to steal sheep either by deception or force. They stole sheep by deception through their false teachings and would later steal by force when they crucified Jesus. They are not concerned about what is best for the sheep; their only interest is how they can profit from the sheep.
This sad truth is seen very plainly in the way the Pharisees treated the man born blind in John 9. They were not concerned about his well-being. They were not excited that he had been given sight. They were only interested in how they could use him to get to Jesus. They verbally abuse him and cast him out of the synagogue for delivering an argument in favor of Jesus that they cannot overthrow. Truly, these are not the actions of genuine shepherds but of thieves and robbers! Jesus, on the other hand, not only cared for this man physically by giving him sight, but He also took the time to guide the man spiritually.
It was not unusual for several flocks to be kept in one fold over night. In an enclosed area it was possible for one man (i.e., the doorkeeper; cf. John 10:3) to watch the sheep while the shepherds rested elsewhere. When a shepherd would return for his flock, the doorkeeper would open the door to the fold. The shepherd would call "his own sheep by name" and lead them out of the fold.
In this illustration, Jesus is the door and shepherd, the sheep are His disciples, and ultimately the fold will be His church. Scholars are not agreed as to whom the doorkeeper represents. The most likely choice would be God the Father although cases can also be made for Moses or John the baptizer. Since the doorkeeper is not mentioned further in this illustration, it appears to be unimportant to specifically identify whom it represents.
The shepherd would physically lead the way and only those sheep who were familiar with his voice would follow him out of the fold. Those who hear the shepherd's voice and follow him are his sheep (cf. John 10:27).
When a shepherd leads his sheep, he will call out loudly from time to time to reassure the flock of his presence. They have come to know his voice and will continue following him. However, if a stranger calls, they will stop and lift their heads in alarm. If the stranger calls again, they will turn and flee because they do not know his voice.
The Pharisees were basically "strangers" in that they desired to lead the flock of God, but they did not do so properly (cf. Matt. 9:36). As a result, many fled from them and to Jesus. Today, we must not listen to "strangers" (i.e., false teachers) and be drawn away from the truth. We must be Jesus' sheep; that is, we must hear His voice and follow Him, not the traditions and opinions of men!
The physical components of this "illustration" are certainly understood by the religious leaders. But, they fail to understand the spiritual meaning (cf. John 10:6). Let it be noted that the Greek word used here is distinct from the one translated as "parable" elsewhere. This is an illustration that is factual in its description (both physically and spiritually), but it is not a physical story as parables are. Because of this fact, there is no difficulty in portraying Jesus as both the door and shepherd of the sheep simultaneously (cf. 10:7,11).