The Father so loved that He gave the Son and now we too are expected to give others our love, our will, our time, our resources, our abilities, our very lives.  Brotherly love is essential to the Christian character, and those who do not possess it cannot be called Christians.  One of the greatest examples of non-brotherly love is that of Cain toward his brother Abel.  Cain murdered Abel because of envy, a trait that has no place in the heart of a Christian. John warns believers that they will be hated by the world for the same reason - envy.