The Lord is my shepherd, I shall not be in want.
Sheep are pretty dumb. As a matter of fact, they almost totally incapable of taking care of themselves. I remember when I worked in my first church there was a family that raised sheep. They had many stories of how the sheep would get tangled up in the fence or would get lost in a grove of trees in the pasture. Not being able to find there way out, especially at night, this family shared how they would be awakened by the sound of the sheep crying in the night.
In the twenty-third Psalm, the Psalmist is comparing himself, and ultimately you and I, to sheep. It was an analogy that was probably a bit of an insult to those who heard it many years ago, for they would have been well aware what he was saying is we are all incapable of taking care of ourselves. So incapable, in fact, that we all need a shepherd.
In John 10:11, Jesus calls himself the Good Shepherd. Again basically reminding those who hear these words that we are incapable of taking care of ourselves. In the previous verse, John 10:10, Jesus has just stated that He came to bring us a full and abundant life. That life, that a relationship with Christ offers, is one we cannot get any other way. Just like a shepherd tending to his flock, Jesus came to tend to us and to our needs: Our needs today and our needs eternal.