But God cannot leave the crime unpunished: from the ground on which it has been spilt, the blood of the one murdered demands that God should render justice (cf. Gen 37:26; Is 26:21; Ez 24:7-8). From this text the Church has taken the name of the “sins which cry to God for justice”, and, first among them, she has included willful murder. For the Jewish people, as for many peoples of antiquity, blood is the source of life. Indeed “the blood is the life” (Dt 12:23), and life, especially human life, belongs only to God: for this reason whoever attacks human life, in some way attacks God himself. — from Evangelium Vitae (1995)
At the root of every act of violence against one’s neighbour there is a concession to the “thinking” of the evil one, the one who “was a murderer from the beginning” (Jn 8:44). As the Apostle John reminds us: “For this is the message which you have heard from the beginning, that we should love one another, and not be like Cain who was of the evil one and murdered his brother” (1 Jn 3:11-12). Cain’s killing of his brother at the very dawn of history is thus a sad witness of how evil spreads with amazing speed: man’s revolt against God in the earthly paradise is followed by the deadly combat of man against man.
After the crime, God intervenes to avenge the one killed. Before God, who asks him about the fate of Abel, Cain, instead of showing remorse and apologizing, arrogantly eludes the question: “I do not know; am I my brother’s keeper?” (Gen 4:9). “I do not know”: Cain tries to cover up his crime with a lie. This was and still is the case, when all kinds of ideologies try to justify and disguise the most atrocious crimes against human beings. “Am I my brother’s keeper?”: Cain does not wish to think about his brother and refuses to accept the responsibility which every person has towards others. We cannot but think of today’s tendency for people to refuse to accept responsibility for their brothers and sisters. Symptoms of this trend include the lack of solidarity towards society’s weakest members-such as the elderly, the infirm, immigrants, children- and the indifference frequently found in relations between the world’s peoples even when basic values such as survival, freedom and peace are involved.