Brothers and Sisters

We frequently hear the people of Christ referred to as "Brothers" or "Brethren". Our sisters (or "Cistern," to believe one proposal related out of a certain church's annual conference) are not as often mentioned so, and yet are similarly referred to. What does the Bible then have to say about this peculiar adoption relationship?

"Do not sharply rebuke an older man, but {rather} appeal to {him} as a father, {to} the younger men as brothers, the older women as mothers, {and} the younger women as sisters, in all purity."
           - 1 Timothy 5:1-2

This is the verse that most people would reference to describe the idea that we are to treat our fellow Christians as members of the family. Brothers and sisters, fathers and mothers. A good model for respect toward our fellows, presuming our family relationships are in the least intact. But Paul is here instructing Timothy on the respect necessary to gently correct erring members of the congregation -- does this apply to those of us not in positions of authority as Timothy was?

"And we know that God causes all things to work together for good to those who love God, to those who are called according to {His} purpose. For those whom He foreknew, He also predestined {to become} conformed to the image of His Son, so that He would be the firstborn among many brethren...."
           - Romans 8:28-29

The Bible tells us that Christ is the firstborn of many brethren -- He is Lord and Savior, but also Brother and Friend. I think we sometimes let one side or the other subsume our mental conception of Him -- the same risk that arises with the Father. But here, we see Christ as the eldest of a brotherhood in relation to the father which we all share. We are made siblings to each other and joint children of the Father.

"For all who are being led by the Spirit of God, these are sons of God. For you have not received a spirit of slavery leading to fear again, but you have received a spirit of adoption as sons by which we cry out, 'Abba! Father!' The Spirit Himself testifies with our spirit that we are children of God, and if children, heirs also, heirs of God and fellow heirs with Christ, if indeed we suffer with {Him} so that we may also be glorified with {Him.}"
           - Romans 8:14-17

We are the children of God adopted into His family through Christ's sacrifice. There is no need for us to see each other as strangers -- merely siblings we don't yet know as well as we might like. And suddenly, with the perspective that we're dealing with a sibling, bound not by our parents' blood, but by His blood, things are a lot different. At least, they should be. We'll be more forgiving of a sibling than of a stranger. We'll be more willing to be honest. In short, we'll love them.

"We love, because He first loved us. If someone says, 'I love God,' and hates his brother, he is a liar; for the one who does not love his brother whom he has seen, cannot love God whom he has not seen. And this commandment we have from Him, that the one who loves God should love his brother also."
           - 1 John 4:19-21