Sheepherding was big business in the ancient world. Farmers weren't able to look after their sheep by themselves and still maintain the farm, so they hired out shepherds to do the job. A shepherd would be expected to lead a large flock of sheep where they needed to go and protect them out in the pasture. Wolves, looking for a tasty snack, or thieves, looking to snag themselves some nice wool sweaters, might come by at any time, and a shepherd had to be ready.
Would-be prophets loved to use songs and stories with pastoral metaphors to brag about their flock-leading skills. But not all "shepherds" were created equal and listeners had to be careful they weren't getting fleeced.
Jesus calls himself "the good shepherd," because, unlike those minimum wage sheepherders who take off at the first sign of danger, Jesus is willing to go to bat for his flock. Since all his sheep personally belong to him, he's ready to defend them—to the death if necessary. He also knows them so well that leading them is no big deal. Jesus can call every sheep by its name and they all recognize his voice and go where he asks (10:3).
Okay, let's un-metaphor ourselves for a moment.
The flock of sheep is made up of people who believe in Jesus, and it's a pretty inviting group. Anyone can be part of it as long as they put their faith in the Jesus. And Jesus is sure that he will be able to lead all of them toward a life with God (10:16).
And in the final scenes of the Gospel, the sheep come back again. Peter redeems himself by affirming his love for Jesus, and Jesus gives Peter the job of taking care of his sheep (21:15-19). With Jesus soon to be gone, he will need some well-trained shepherds to lead and protect his flock—i.e., his believers.
Shepherds aren't unique to the gospels, that's for sure. They're everywhere in the Bible. What can we say? The people of Judea loved them some wool sweaters.
You've probably heard the phrase "The Lord is my shepherd," right? Well, that's the Bible talking—Psalm 23 to be exact. In that case, God is leading the psalmist like a sheep into calm and beautiful meadows. Now it's your turn: go find more Bible shepherds. We dare you.
Muhammad, the founder of Islam, was also a shepherd and ended up leading a pretty big flock himself—1.5 billion Muslims worldwide. Yowza.
It's not always a worldwide-religion creating image, though. In the novel Animal Farm, the sheep characters show the negative side of all this pastoral imagery. They mindlessly bleat slogans in favor of their chief, a critique of human "sheep" who blindly follow a charismatic leader.
There. That wasn't so baaaaad, was it? (Sorry, we had to.)