While I was with them, I kept them in your name, which you have given me. I have guarded them, and not one of them has been lost except the son of destruction, that the Scripture might be fulfilled. But now I am coming to you, and these things I speak in the world, that they may have my joy fulfilled in themselves. I have given them your word, and the world has hated them because they are not of the world, just as I am not of the world. I do not ask that you take them out of the world, but that you keep them from the evil one. They are not of the world, just as I am not of the world. Sanctify them in the truth; your word is truth.
What do you think the Lord Jesus means when he says "They are not of the world". Certainly he is not saying that his disciples are not human or look different than others.
I think that he is speaking to the issue of identity and, in specific, spiritual identity. Those who have been born of the spirit are different than those who have not been born again.
For such as these the world is not home. The scriptures tell us that our citizenship is in heaven and our desire is to see the kingdom of God come on earth as it is in heaven. The heart of this is not theological but spiritual. We are in a daily spiritual battle and the evil one opposes us at every turn. It is why we the sanctification that comes through God's word.
Your word is truth Lord. Help me to be changed by it as I read and study your word.