Oh Brother

Ever been to church, or heard Christians refer to each other as brother or sister? You'll hear maybe the pastor introduce a special speaker as Brother Brad, or Sister Sue. I don't really get that? I have a brother and sister, I rarely - actually I've never referred to either of them as Brother Ricky, or Sister Rachel. Why do Christians do this? "Because were brothers and sister in Christ". Were also all humans, and creations of God. We don't call each other fellow human, or creation person. I guess it just makes the special guest feel better. Anyway brothers and sisters in Christ... I'll never call any of you this in person.