Behold, how great a love the Father has bestowed on us, that we should be called children of God! For this cause the world doesn't know us, because it didn't know him.
The reason for the world's hatred of Christians lies in their hostility to all truth and righteousness.  They did not recognize Jesus Christ as the Son of God. John's statement here, that the world did not know him, means that, "Although they saw the human Jesus, they did not recognize him as the Son of God."[8] In connection with the rejection of himself, Christ foretold the hatred of his followers (John 16:3); and in the holocaust so soon coming upon the Christians, the same root hatred of the light was assigned here as the reason behind it.