Love is a characteristic of God’s people, because it is an intrinsic quality of God Himself (1 John 4:8).  John has just been using Cain as an example of someone who did not love his brother, Abel (Genesis 4:1-12; 1 John 3:11-13).  Murdering Abel was shockingly wicked, and its deadly echo has reverberated down through the centuries.  That dreadful act of hatred was an epic example of being against God's family and therefore against God.  

By contrast, the believers who made up the Early Church found that, despite differences in background, ethnicity, language, culture and finances, they learned to love each other (John 15:9-13; 1 Peter 1:22).  They found they had a supernatural desire to share sacrificially and give to people who ordinarily they might never have chosen as friends (Acts 4:32-35).  That was evidence that they had moved from the dominion of death to the Kingdom of Light (Colossians 1:13).

Yet there were some in the church who did not love like that.  They deeply resented some leaders or members of the church and tried to influence other people in the church against them.  It was a sign that, although they were in the church, they were not in Christ.  They were harbouring the 'spirit of Cain' in their midst.  Such people were trusting in Jesus, they were not spiritually alive but remained under condemnation (John 3:36): whatever they may have said about Jesus they were not trusting Him alone for their salvation (John 3:18-21).

It is good to check ourselves and observe the dynamics in the church to see that we are 'on-side' with God.  The test is whether we have a desire for fellowship with those who the Lord has placed us among.  The same test is for others too, whether they have a desire for fellowship.  If they will not stay, they may never have truly belonged (1 John 2:19).  Beware, because churches attract power-seekers and anti-Christs – they try to capture the attention of people who will exalt them; but they do not love as Christ loved.  True members of God’s family give themselves wholeheartedly and sacrificially to others who are not like them, because they seek to be like Christ.  Take the test, and see how you measure up, before weighing up the dynamics in the local church.