What makes Jesus the Good Shepherd?

3 So he told them this parable: 4 “What man of you, having a hundred sheep, if he has lost one of them, does not leave the ninety-nine in the open country, and go after the one that is lost, until he finds it? 5 And when he has found it, he lays it on his shoulders, rejoicing. 6 And when he comes home, he calls together his friends and his neighbors, saying to them, ‘Rejoice with me, for I have found my sheep that was lost.’ 7 Just so, I tell you, there will be more joy in heaven over one sinner who repents than over ninety-nine righteous persons who need no repentance (Lk 15:3-7).

“Truly, truly, I say to you, he who does not enter the sheepfold by the door but climbs in by another way, that man is a thief and a robber. 2 But he who enters by the door is the shepherd of the sheep. 3 To him the gatekeeper opens. The sheep hear his voice, and he calls his own sheep by name and leads them out. 4 When he has brought out all his own, he goes before them, and the sheep follow him, for they know his voice. 5 A stranger they will not follow, but they will flee from him, for they do not know the voice of strangers.” 6 This figure of speech Jesus used with them, but they did not understand what he was saying to them.

7 So Jesus again said to them, “Truly, truly, I say to you, I am the door of the sheep. 8 All who came before me are thieves and robbers, but the sheep did not listen to them. 9 I am the door. If anyone enters by me, he will be saved and will go in and out and find pasture. 10 The thief comes only to steal and kill and destroy. I came that they may have life and have it abundantly. 11 I am the good shepherd. The good shepherd lays down his life for the sheep. 12 He who is a hired hand and not a shepherd, who does not own the sheep, sees the wolf coming and leaves the sheep and flees, and the wolf snatches them and scatters them. 13 He flees because he is a hired hand and cares nothing for the sheep. 14 I am the good shepherd. I know my own and my own know me, 15 just as the Father knows me and I know the Father; and I lay down my life for the sheep. 16 And I have other sheep that are not of this fold. I must bring them also, and they will listen to my voice. So there will be one flock, one shepherd. 17 For this reason the Father loves me, because I lay down my life that I may take it up again. 18 No one takes it from me, but I lay it down of my own accord. I have authority to lay it down, and I have authority to take it up again. This charge I have received from my Father.” (Jn 10:1-18).

What makes Jesus a good shepherd? His determination and ability to protect his sheep. Not one will be forever lost. If his flock loses sheep, then he failed. He failed to protect his sheep from deadly harm. 

Now, a freewill theist might say Jesus protects his sheep so long as they remain within eyeshot of the shepherd, but if they separate themselves from the flock, they expose themselves to danger. Jesus doesn't protect them from wandering away of their own accord. 

But that's what endangers sheep. If they stray, the wolf can pick them off because they are too far away for the shepherd to protect them. So protecting the sheep must include reclaiming stray sheep–otherwise it's no protection at all. The peril lies in getting separated from the shepherd. And that's why the shepherd retrieves sheep that wander off.

A freewill theist might object that I'm pressing the metaphor. It's just a metaphor. Every analogy has limitations. 

That's true, but what else is there to the metaphor of sheep and shepherds? It's chosen to illustrate a principle since it plays on the popular stereotype of lost sheep, endangered sheep. That's what sheep do. Left to their own devices, they wander off into the waiting jaws of the bear or the wolf pack. And the job of a shepherd is to protect the flock. In the OT, David is the paradigmatic shepherd who protected his flock from wild predators. Does Jesus do less for his sheep than David?