Digest of terms
Though by no means exclusive to Christianity, in the West the notion has been strongly resourced from that tradition. Paul in the New Testament regularly addresses his fellow Christians as "brothers and sisters", while in the epistles of John love of 'brethren' is urged repeatedly, and this has persisted over the centuries. It carried over into the trade union movement, reflecting its Christian inspiration; members met in their branches known as chapels and used the terminology of brothers.
From outside a biblical perspective as well there is the implication that from the beginning of human civilisation the loyalty and warmth of affection between brothers are qualities which should characterise all human relationships, even if commonly missing even within immediate families (not just between Cain and Abel, but in comparable tales from ancient Africa, China and India). Affirmation of the positive values of brotherliness and sisterliness was made in secular terms in the French Revolution with its slogan of Liberty, Equality and Fraternity. The more common term today is 'solidarity'. It conveys a strong prizing of the organic interdependence of all humanity, with an associated commitment to mutual support and celebration.