Brotherhood simultaneously unites and divides people. In the impossibility of discovering a true unifying principle, brotherhood becomes either abstract, and therefore insignificant, or ideological, and therefore dangerous. Both directions lead to the disappearance of true brotherhood from people’s lives. Following the thought of Joseph Ratzinger, the main thesis of the article is that the Christian brotherhood is the only true, universal and permanent unity of people. The prologue of such understanding is the Old Testament theology of election, at the center of which is man’s salvational share in Christ’s Sonship and his brotherhood with all people. Therefore, God’s Fatherhood and Christ’s salvation of all people are precursory strengths of Christian brotherhood. In this perspective, the duality between brothers and those that are not is shown in the service of true universalism. The direct brothers – in the light of the cross of Christ – recognize their election as agency and mission to the non-brothers. This confirms Christian brotherhood as a real unity of mankind, and thus as a foundational theological category in understanding Christ’s gift of salvation and the mission of His Church.