When a shepherd needed to stop for a while, the Hebrew people would set-up a stone pen with an opening at one end. One way in, one way out and a shepherd as the gate. The sheep would be accounted for by not being able to pass the shepherd unaware and predators would have to go through the shepherd first to get to the flock.
He will come in and go out, and find pasture. (John 10:9)
"I am the good shepherd. The good shepherd lays down his life for the sheep. The hired hand is not the shepherd who owns the sheep. So when he sees the wolf coming, he abandons the sheep and runs away. Then the wolf attacks the flock and scatters it. The man runs away because he is a hired hand and cares nothing for the sheep. "I am the good shepherd; I know my sheep and my sheep know me-- just as the Father knows me and I know the Father--and I lay down my life for the sheep. (John 10:11-15)
When a shepherd calls to his sheep in his sheep-pen to go out and find grazing pasture, they know his voice. With his company the sheep have heard him speaking with others, yelling at predators, singing a heart-felt melody, or naming the new sheep on the block - they know his voice. So, when the shepherd orders for them to rise and go out to pasture, they go. Should the shepherd's sheep be mixed in the pasture with other sheep and it is time to travel on, even then when the shepherd calls the sheep, they will follow out of the mix because they know his voice. Beware the "hired hand" - the "hired hand" is NOT da man!
Jesus Christ is not only The Shepherd (our Shepherd, the Believer's Shepherd), He is The Good Shepherd and The Gate!