Genesis 9:6 Updated American Standard Version (UASV)
6 “Whoever sheds man’s blood,
By man his blood shall be shed,
For in the image of God
he made man.
Exodus 21:12 Updated American Standard Version (UASV)
12 “He who strikes a man so that he dies shall be put to death.
As can be seen from the above, the penalty for willfully taking the life of another is the death penalty. We see from the account concerning Cain that he not only did not receive the death penalty for murdering his brother Abel, but he was given protection from anyone seeking to avenge that murder.―Genesis 4:15.
At first glance, this may seem like an inconsistency on the part of Jehovah’s justice, but it is not. There are multiple reasons as to why Cain did not receive the death penalty. At the time of this murder, God had not established the death penalty for the murder of another. (Rom 13:1-4) It was only after, “the LORD saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually.” (Gen 6:5) After the destruction of the Nephilim and wicked man by means of the flood, did God say, “”Whoever sheds the blood of man, by man shall his blood be shed . . .”―Genesis 9:6.
Jehovah is the giver of life and death, and he rightly chose to give Cain a life sentence of banishment. (Deut. 32:39) However, God did express his thoughts that Cain was worthy of death. Jehovah said, “What have you done? The voice of your brother’s blood is crying to me from the ground.” (Gen. 4:10) Even Cain himself knew that death was the possibility, and asked Jehovah for protection. Cain said to the Jehovah, “My punishment is greater than I can bear. Behold, you have driven me today away from the ground, and from your face, I shall be hidden. I shall be a fugitive and a wanderer on the earth, and whoever finds me will kill me.” (Gen. 4:13-14) In addition, the death penalty then was made known as an option, for the taking of a life, as Jehovah said, “If anyone kills Cain, vengeance shall be taken on him sevenfold.” (Gen. 4:15) Therefore, due to mitigating circumstances, Cain is the exception to the rule, and cannot be used against the justice of the death penalty that was to become a part of human law after the flood.