'The voice of blood,' as in Genesis 4:10, signifies violence to charity. There are several passages in the Word where the word 'voice' is used for accusation, and 'blood' is used for sins, particularly hatred. Whoever holds hatred towards his brother kills him in his heart, as the Lord teaches in Matthew 5:21-22 and elsewhere.

(Referenties: Arcana Coelestia 375)