54 Absorbed and deepened in the family, faith becomes a light capable of illumining all our relationships in society. As an experience of the mercy of God the Father, it sets us on the path of brotherhood. Modernity sought to build a universal brotherhood based on equality, yet we gradually came to realize that this brotherhood, lacking a reference to a common Father as its ultimate foundation, cannot endure. We need to return to the true basis of brotherhood. The history of faith has been from the beginning a history of brotherhood, albeit not without conflict. God calls Abraham to go forth from his land and promises to make of him a great nation, a great people on whom the divine blessing rests (cf. Gen 12:1-3). As salvation history progresses, it becomes evident that God wants to make everyone share as brothers and sisters in that one blessing, which attains its fullness in Jesus, so that all may be one. The boundless love of our Father also comes to us, in Jesus, through our brothers and sisters. Faith teaches us to see that every man and woman represents a blessing for me, that the light of God’s face shines on me through the faces of my brothers and sisters. How many benefits has the gaze of Christian faith brought to the city of men for their common life! Thanks to faith we have come to understand the unique dignity of each person, something which was not clearly seen in antiquity. In the second century the pagan Celsus reproached Christians for an idea that he considered foolishness and delusion: namely, that God created the world for man, setting human beings at the pinnacle of the entire cosmos. "Why claim that [grass] grows for the benefit of man, rather than for that of the most savage of the brute beasts?" "If we look down to Earth from the heights of heaven, would there really be any difference between our activities and those of the ants and bees?" At the heart of biblical faith is God’s love, his concrete concern for every person, and his plan of salvation which embraces all of humanity and all creation, culminating in the incarnation, death and resurrection of Jesus Christ. Without insight into these realities, there is no criterion for discerning what makes human life precious and unique. Man loses his place in the universe, he is cast adrift in nature, either renouncing his proper moral responsibility or else presuming to be a sort of absolute judge, endowed with an unlimited power to manipulate the world around him.
Source: Lumen Fidei (Vatican.va)