John 17:16-19 ESV
They are not of the world, just as I am not of the world. Sanctify them in the truth; your word is truth. As you sent me into the world, so I have sent them into the world. And for their sake I consecrate myself, that they also may be sanctified in truth.
We are in the world, but not of the world. It is the truth that makes the separation, that divides the light from the darkness. God sent His Son into the world for this purpose and the Son sends us out into the world for this same purpose.
He has fulfilled all holiness that we might be holy. We have become the sent ones of God to be the children of light, the light of the truth.
We have become one with the way, the truth, and the light.