Like any pair of siblings, my younger brother and I fought quite a bit growing up. We clashed fiercely and frequently over the vital issues of boyhood: who crossed the line in the back seat of the car, whether the pitch was a ball or a strike, and whether the little collision before the football landed was pass interference. To the best of my memory, however, I only fought twice with people other than my brother, and both fights were because someone was picking on him.

For those of you who grew up with siblings, the chances are good that you never fought with anyone as frequently as you did with your siblings. The chances are also good, however, that you never fought on someone’s behalf as fiercely as you did for your siblings. For most people, there’s a natural affection beneath sibling rivalry that doesn’t surface until one of two things happen: (1) your sibling is threatened, or (2) you move out of the house.

Over the past few months, this column has included discussions on a whirlwind of virtues: faith, moral excellence, mature knowledge, self-control, perseverance and godliness. Each of these character traits primarily pertains to the way we relate to God as individuals. The next virtue in 2 Peter 1:5-7 involves our relationships with others in a way that none of the other character traits do. The Greek word is the same word for which the city of Philadelphia is named. The word refers to the natural affection and loyalty between siblings, and Peter tells his readers that they are to add brotherly affection to godliness. We are to extend the same affection and loyalty toward our fellow Christians that we naturally have toward our siblings. Peter says for us to relate to each other not only as associates or fellow church members, but as brothers and sisters. If you believe in Jesus Christ, you have more in common with a believer who is a different race or generation than you do with an unbelieving family member.

How might we add brotherly affection to our lives? Paul gives some instructions along these lines to believers in 1 Thessalonians 4:9-12. They are to live peacefully with one another, refuse to gossip, and try not to be financially dependent on others. The author of Hebrews also gives some instructions in chapter 13: Respect your leaders, remain faithful in marriage, and visit believing prisoners. An early pastor of Rome, Clement, also exhorts the church in Corinth to repent of their lack of brotherly affection. They had fired their pastors who were men of character.

The command to add brotherly affection to our lives is more countercultural than one might first think. In addition to our political, racial and economic divisions, many cultural commentators have noticed that one of the ways we are segregated most is according to age. Few opportunities exist for senior citizens to spend time with millennials, and neither group spends much time with unrelated children outside of work. Life in church, however, should be much different (Titus 2:1-10). When people from different age and socioeconomic groups relate as brothers and sisters, the world will see that our commitment and affection toward our spiritual siblings is not natural, but supernatural.