Genesis 4:10

What hast thou done? The tactful, indirect approach having proved unavailing, God proceeded to charge Cain with his crime. The question “What hast thou done?” implied perfect knowledge of the facts.

The voice of thy brother’s blood. The trembling murderer found an all-seeing and all-knowing God reading his naked soul. How could He who notes the sparrow’s fall, He who is the author of life, be deaf to the silent cry of the first martyr (see Ps. 116:15)? Blood is life, and as such is precious to the great Giver of life (Gen. 9:4).

Against all the inhumanity of man toward his fellow men down through the intervening ages, the cry of Abel ascends to God (Heb. 11:4). Abel met his death at the hand of a near kinsman. Similarly, Jesus, coming to this earth as a kinsman to the human race, was rejected and sent to His death by His brethren.