1 While the Lord is still speaking to the Father, and praying for His disciples, He says: “I have given them Your saying; and the world has hated them.” That hatred they had not yet experienced in those sufferings of their own, which afterwards overtook them; but He speaks thus in His usual way, foretelling the future in words of the past tense. And then, subjoining the reason of their being hated by the world, He says, “Because they are not of the world, even as I am not of the world.” This was conferred on them by regeneration; for by generation they were of the world, as He had already said to them, “I have chosen you out of the world.” It was therefore a gracious privilege bestowed upon them, that they, like Himself, should not be of the world, through the deliverance which He was giving them from the world. He, however, was never of the world; for even in respect of His servant-form He was born of that Holy Spirit of whom they were born again. For if on that account they were no more of the world, because born again of the Holy Spirit; on the same account He was never of the world, because born of the Holy Spirit.
Source: Tractates on the Gospel of John (New Advent)