Genesis 4:15 And the Lord said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the Lord set a mark upon Cain, lest any finding him should kill him. 16 And Cain went out from the presence of the Lord, and dwelt in the land of Nod, on the east of Eden.
[Patriarchs & Prophets pp 78] Notwithstanding that Cain had by his crimes merited the sentence of death, a merciful Creator still spared his life, and granted him opportunity for repentance. But Cain lived only to harden his heart, to encourage rebellion against the divine authority, and to become the head of a line of bold, abandoned sinners. This one apostate, led on by Satan, became a tempter to others; and his example and influence exerted their demoralizing power, until the earth became so corrupt and filled with violence as to call for its destruction.
In sparing the life of the first murderer, God presented before the whole universe a lesson bearing upon the great controversy. The dark history of Cain and his descendants was an illustration of what would have been the result of permitting the sinner to live on forever, to carry out his rebellion against God. The forbearance of God only rendered the wicked more bold and defiant in their iniquity. Fifteen centuries after the sentence pronounced upon Cain, the universe witnessed the fruition of his influence and example, in the crime and pollution that flooded the earth.
It was made manifest that the sentence of death pronounced upon the fallen race for the transgression of God's law was both just and merciful. The longer men lived in sin, the more abandoned they became. The divine sentence cutting short a career of unbridled iniquity, and freeing the world from the influence of those who had become hardened in rebellion, was a blessing rather than a curse.
Ecclesiastes 8:11 Because sentence against an evil work is not executed speedily, therefore the heart of the sons of men is fully set in them to do evil.
May The Lord add His blessing to the study of His word. God bless!