5 Therefore said He, “I am from above. You are of this world: I am not of this world. I said therefore unto you, that you shall die in your sins.” He has explained to us, brethren, what He wished to be understood by “you are of this world.” He said therefore in fact, “You are of this world,” because they were sinners, because they were unrighteous, because they were unbelieving, because they savored of the earthly. For what is your opinion as regards the holy apostles?
What difference was there between the Jews and the apostles? As great as between darkness and light, as between faith and unbelief, as between piety and impiety, as between hope and despair, as between love and avarice: surely the difference was great. What then, because there was such a difference, were the apostles not of the world? If your thoughts turn to the manner of their birth, and whence they came, inasmuch as all of them had come from Adam, they were of this world. But what said the Lord Himself to them? “I have chosen you out of the world.” Those, then, who were of the world, became not of the world, and began to belong to Him by whom the world was made. But these men continued to be of the world, to whom it was said, “You shall die in your sins.”
Source: Tractates on the Gospel of John (New Advent)