1 John 3:10

1 John 3:10 says, In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.  John said we could tell who was of God and who was of the Devil by the way they lived in the world.  He said that those who did not live righteously and didn't love their brother were of the Devil and not of God.  Our faith in Jesus Christ should set us apart from non-believers, even if we occasionally fail.  

Verse eleven adds, For this is the message that ye heard from the beginning, that we should love one another.  John once again emphasizes that as Christians, we should love one another.  This means all people and not just the ones we like and who are like us.  We may not like their actions, but we should still love them and want them to be redeemed.  

Verse twelve continues, Not as Cain, who was of that wicked one, and slew his brother. And wherefore slew he him? Because his own works were evil, and his brother's righteous.  John then gave the example of Cain, who he said was of the evil one, and killed his brother Abel, who was righteous.  As followers of Christ, we should be like Abel and not like Cain. 

Verse thirteen concludes, Marvel not, my brethren, if the world hate you.  John said we should not be amazed if the people of the world, those who are not Christians, hate us.  They hated and killed Jesus Christ, but He still loved them and died for them as well.  We need to have the same love for all people.