He uses this word over and over again. Paul must have good reasons for this. Why does he do it?
In that culture, brothers and sisters held deep, permanent, and intimate relationships. These were some of the strongest (if not the strongest) bonds in that society.
Paul could have repeatedly used the word "friends." Instead, he chose "brothers." Why?
I believe Paul was stressing both intimacy and permanence. He may have had other reasons as well, but these two seem to be a big part of his intent.
Genetic brothers and sisters, for all their problems, have both intimate and permanent relationships. There is a certain level of familiarity and care that we have with siblings that is unique to those relationships. Also, sibling relationships last our entire lives. Even though we may have squabbles, nothing severs the brotherhood bond.
Paul's use of this term, therefore, should inform the way we think of the church. For example, how close are we really with our brothers and sisters in Christ? Do we really know each other or are our relationships more surface-level? If we are going to be siblings in Christ, then we need to get into the messy, personal, tough, real aspects of one another's lives. I don't know how to do this other than spend time together, open up to one another, serve one another, be served by one another, and be authentic with one another.
Paul also expected permanence of relationships. Siblings don't stop being siblings. Church family doesn't stop being church family. When we think of the church in terms of everlasting relationships, this dramatically affects how we handle both the good times and the bad. Unity is non-negotiable. We work through all aspects of life. Division is not an option.
In our lives we may move from place to place for whatever reason. We may also be parts of different bodies of believers. Despite this, let's think of the church as God does: a unified whole. We must remain united with the whole.
As I think about these things, I'm filled with joy. God, in His great blessings, has caused us to be part of His redeemed family. He desires that we be perfectly united in authentic relationships with one another founded upon Him. All to His glory.
Now to the nitty-gritty work. Effort is required to get to know one another at a real level. However, since these relationships are permanent we may as well get started.
How we think about the church greatly impacts how we live as the church (obviously). Let's all think through the lens of intimacy and permanence.