The word picture Jesus gives us in John 10 of Jesus as the shepherd and his followers as sheep is pretty compelling on several levels. I'll name a few:
1. Sheep don't think a lot. OK, let's tell the truth: they're downright stupid. I don't have any sheep...never owned any sheep. I petted a sheep at the zoo a few times, but that's about the extent of my sheep exposure. However, I do have chickens. I know, one's a bird and the other is a mammal, but in terms of intelligence, I think they're probably pretty similar. My 8 hens walk through their water bowl EVERY time and then look at me like, "hey, the water's dirty!" If I didn't have them in a pen, they'd all be dead, because they're really easy prey for hawks, coyotes, foxes, etc. Even the way they look at me, you can tell there's just not that much going on upstairs. They require someone to look out for them, protect them, provide for their needs. And in spite of their laughable ignorance, they know my voice and come running when I'm near.
That's what Jesus is talking about with the sheep. We might think we're smart, but for'smart' people, we sure do get ourselves in a lot of trouble. We do stupid things and for all our knowledge, we really don't know all that much.
Jesus is saying that we are like sheep. We need care and protection. If we'll do what He tells us, we'll be spiritually safe and nurtured.
2. There is only one way into the pen. People really struggle with this, and I'll talk about it further in chapter 14, but I think Jesus is talking about the 'way to God' here. He's saying that He is the Son of God, and you only get in through Him. He'll affirm this elsewhere in John.
3. The shepherd's life was the most humble of any family position in society. It was a dirty, nasty, uncomfortable job. Jesus lived a life of humility, and he's the example we follow. My attitude is supposed to be one that says, "I'm not above anything that God wants me to do."
4. Shepherds protect the sheep at all costs. Hired hands do not. I used to own my own business and I had some great managers along the way who worked for me. But at the end of the day, nobody cared about my business like I did. It was my baby. I'd go way above and beyond any normal requirement for it. Others cared, yes, but at the end of the day, it was still just a job for them.
I know this is long already, but let me also alert you to one other thing. In v. 22, there is a reference to the Feast of Dedication. This feast is a result of the cleansing of the temple by a man named Judas Maccabeus in 164 B.C. You will not find this story in the Bible, unless you have a Catholic Bible. There is a body of around 14 books that were of questionable spiritual value and, therefore, not included in the Bible. These make up a body of work we call the Apocrypha. Some of these books are far out. Bel and the Dragon, for instance (No, not puff the magic dragon). But other books DO give us important historical information would would otherwise not have. This is the case for the the Maccabees series. There are 4 books (1Maccabees, 2Maccabees, etc.). I own an Apocrypha, have read it more than once, and refer to it from time to time. I do not preach from it, though, as it is not the Canon (THE Bible).
All that is to say that you would benefit from having one and reading it, just so you can know what's there and how it affects the thinking and teaching in the rest of the Bible. Some important history happens in the Apocrypha that answers some questions for us. But this reading is really for those who have a good grasp of the Bible and want to really understand what's going on.