To our godliness we are to add brotherly affection and love. We struggle with this one. Instead of demonstrating brotherly affection, we are lucky if we can muster up some "brotherly tolerance." Many Christians will say things like, "I love my brother, but I don't like them." They think it is biblically acceptable to dislike their brother.
Peter emphasizes that the believer in Jesus Christ is to supplement his faith with certain qualities. So far, we have seen that we are to add virtue, knowledge, self-control, steadfastness, and godliness. This addition of brotherly affection is not easy. Because we are sinful creatures we discover that our brother or sister in Christ does things that hurt and offend us.