What is a Brother?

"To be Brother of Christ; to be Brother of each other in community life; and to be Brother of all people without distinction, especially the poorest".

... "These religious brothers are called to be brothers of Christ, deeply united with him, 'the firstborn among many brothers' (Rom 8:29), brothers to one another, in mutual love and working together in the Church in the same service of what is good; brothers to everyone, in their witness to Christ's love for all, especially the lowliest, the neediest; brothers for a greater brotherhood in the Church."

“By living in a special way this aspect of Christian and consecrated life, religious brothers proclaim to all the Lord's words: "And you are all brothers" (Mt 23:8).
From Jean-Paul II in Vita Consecrata.