1 John 5:19
 We know that we are from God, and the whole world lies in the power of the evil one. (ESV)
Us and them. The Apostle John makes a very clear distinction between two groups of humanity. People are either from God, or in the power of the evil one. This is a distinction that many people have a problem with. If you hold to a belief that man is basically good in his nature what the Apostle John says will be repugnant to you.
John has established all throughout this epistle that the only people who are from God are those who have believed in Jesus Christ. There are those who look at the requirement of believing in Jesus Christ as an optional one. They feel that they should be able to believe whatever they want about who God is and who Jesus is without being excluded from a relationship with God.
1 John 2:23
 No one who denies the Son has the Father. Whoever confesses the Son has the Father also. (ESV)
The world has denied the Son. They may say that Jesus existed, but they refute his deity. The world will allow for a belief that Jesus was a prophet. They will say he was a teacher. They will say he was a leader. But, the world stands apart from the children of God because of their refusal to place their faith in Jesus Christ as the only Son of God, and the only way to right relationship with God. I will close with this famous quote from the great C. S. Lewis:
“I am trying here to prevent anyone saying the really foolish thing that people often say about Him: I’m ready to accept Jesus as a great moral teacher, but I don’t accept his claim to be God. That is the one thing we must not say. A man who was merely a man and said the sort of things Jesus said would not be a great moral teacher. He would either be a lunatic — on the level with the man who says he is a poached egg — or else he would be the Devil of Hell. You must make your choice. Either this man was, and is, the Son of God, or else a madman or something worse. You can shut him up for a fool, you can spit at him and kill him as a demon or you can fall at his feet and call him Lord and God, but let us not come with any patronizing nonsense about his being a great human teacher. He has not left that open to us. He did not intend to.”
― C.S. Lewis, Mere Christianity