The true deceptive character of Satan had to be fully revealed before evil could be eradicated. The first example of his enmity was between Cain and Abel recorded in Genesis 3:15.
“The murder of Abel was the first example of the enmity that God had declared would exist between the serpent and the seed of the woman—between Satan and his subjects and Christ and His followers. Through man’s sin, Satan had gained control of the human race, but Christ would enable them to cast off his yoke. Whenever, through faith in the Lamb of God, a soul renounces the service of sin, Satan’s wrath is kindled. The holy life of Abel testified against Satan’s claim that it is impossible for man to keep God’s law. When Cain, moved by the spirit of the wicked one, saw that he could not control Abel, he was so enraged that he destroyed his life. And wherever there are any who will stand in vindication of the righteousness of the law of God, the same spirit will be manifested against them. It is the spirit that through all the ages has set up the stake and kindled the burning pile for the disciples of Christ. But the cruelties heaped upon the follower of Jesus are instigated by Satan and his hosts because they cannot force him to submit to their control. It is the rage of a vanquished foe. Every martyr of Jesus has died a conqueror. Says the prophet, ‘They overcame him [“that old serpent, called the devil, and Satan”] by the blood of the Lamb, and by the word of their testimony; and they loved not their lives unto the death’ (Revelation 12:11, 9).” Patriarchs and Prophets, 77.
“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.” Ibid., 78.
“In sparing the life of the first murderer, God presented before the whole universe a lesson bearing upon the great controversy. … 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.” Ibid., 78.