Cain did not love his brother Abel. Murdering him was shockingly wicked, and its deadly echo has reverberated down through the centuries (1 John 3:11-13). That dreadful act was an epic example of what it means to be 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 loved each other. They found they had a supernatural desire to share and give to people who ordinarily they might never have chosen as friends.