"‘Very truly, I tell you, anyone who does not enter the sheepfold by the gate but climbs in by another way is a thief and a bandit. The one who enters by the gate is the shepherd of the sheep. The gatekeeper opens the gate for him, and the sheep hear his voice. He calls his own sheep by name and leads them out. When he has brought out all his own, he goes ahead of them, and the sheep follow him because they know his voice. They will not follow a stranger, but they will run from him because they do not know the voice of strangers.’ Jesus used this figure of speech with them, but they did not understand what he was saying to them."
"So again Jesus said to them, ‘Very truly, I tell you, I am the gate for the sheep. All who came before me are thieves and bandits; but the sheep did not listen to them. I am the gate. Whoever enters by me will be saved, and will come in and go out and find pasture. The thief comes only to steal and kill and destroy. I came that they may have life, and have it abundantly.'"The gatekeeper's identity is not clear, but we shouldn't worry too much about this because Jesus is the gate and can open himself. Still, a gatekeeper is in the story and various commentators have their opinions. Matthew Henry in his "Concise Commentary" names the "Spirit of Christ" as the one who opens the gate,
"Here is a parable or similitude, taken from the customs of the East, in the management of sheep. Men, as creatures depending on their Creator, are called the sheep of his pasture. The church of God in the world is as a sheep-fold, exposed to deceivers and persecutors. The great Shepherd of the sheep knows all that are his, guards them by his providence, guides them by his Spirit and word, and goes before them, as the Eastern shepherds went before their sheep, to set them in the way of his steps. Ministers must serve the sheep in their spiritual concerns. The Spirit of Christ will set before them an open door. The sheep of Christ will observe their Shepherd, and be cautious and shy of strangers, who would draw them from faith in him to fancies about him."All of us sheep need to learn how to recognize the shepherd's voice. As far as I can tell, the best way to do this is to study the Bible in the company of other faithful Christians. This also helps us learn how to recognize the thieves and bandits who are always finding a way into the sheepfold around the gate and the gatekeeper.