The main reason of forbidding the eating of blood, doubtless was because the shedding of blood in sacrifices was to keep the worshippers in mind of the great atonement; yet it seems intended also to check cruelty, lest men, being used to shed and feed upon the blood of animals, should grow unfeeling to them, and be less shocked at the idea of shedding human blood. Man must not take away his own life. Our lives are God's, and we must only give them up when he pleases. If we in any way hasten our own death, we are accountable to God for it. When God requires the life of a man from him that took it away unjustly, the murderer cannot render that, and therefore must render his own instead. One time or other, in this world or in the next, God will discover murders, and punish those murders which are beyond man's power to punish. But there are those who are ministers of God to protect the innocent, by being a terror to evil-doers, and they must not bear the sword in vain, Romans 13:4. Wilful murder ought always to be punished with death. To this law there is a reason added. Such remains of God's image are still upon fallen man, that he who unjustly kills a man, defaces the image of God, and does dishonour to him.
Matthew Henry's Commentary on Genesis 9:6
Commentary on Genesis 9:4-7
(Read Genesis 9:4-7)
The main reason of forbidding the eating of blood, doubtless was because the shedding of blood in sacrifices was to keep the worshippers in mind of the great atonement; yet it seems intended also to check cruelty, lest men, being used to shed and feed upon the blood of animals, should grow unfeeling to them, and be less shocked at the idea of shedding human blood. Man must not take away his own life. Our lives are God's, and we must only give them up when he pleases. If we in any way hasten our own death, we are accountable to God for it. When God requires the life of a man from him that took it away unjustly, the murderer cannot render that, and therefore must render his own instead. One time or other, in this world or in the next, God will discover murders, and punish those murders which are beyond man's power to punish. But there are those who are ministers of God to protect the innocent, by being a terror to evil-doers, and they must not bear the sword in vain, Romans 13:4. Wilful murder ought always to be punished with death. To this law there is a reason added. Such remains of God's image are still upon fallen man, that he who unjustly kills a man, defaces the image of God, and does dishonour to him.