God questioned Cain concerning the location of Abel. When Cain failed to provide an honest answer, God demonstrated his omniscience (all-knowingness). He demonstrated that He knew exactly what Cain had done. God replied to Cain's lie:
He said, "What have you done? (Genesis 4:10)As if to say, why have you done this? Look at the result of your actions!
The voice of your brother's blood is crying to Me from the ground. (Genesis 4:10)Your brother. Your very own brother. You murdered your own brother! You cannot hide your crime from God!
This verse also shows that God is not unwatchful. He notices when the righteous suffer. And although God may not act immediately to every murderer as He did to Cain, believers can be assured that justice will ultimately be done. At the great judgment, every crime, no matter how perfectly or discreetly done, will be uncovered. While the righteous often suffer and the wicked often prosper, such will not hold true in the eternal state.
However, to Cain, God provides an immediate punishment, a painful curse. Just as the first sin in the garden had its consequences and curses, so God here makes known to Cain the wickedness of his murderous anger. God sets a curse upon Cain:
Now you are cursed from the ground, which has opened it's mouth to receive your brother's blood from your hand. When you cultivate the ground, it will no longer yield its strength to you, you will be a vagrant and a wanderer on the earth." (Genesis 4:11-12)The ground which took in and absorbed Abel's blood would no longer yield its strength to Cain. That is, the ground would no longer produce at its previous strength. It would no longer bring forth its fruits with the same might and power.
One might think that after all of this, Cain might have been humbled— that he might have seen his sin. Cain, however, was not humbled. Cain did not repent. And in his next reply to God, he is concerned only about himself.
Cain and Abel: Mark of Mercy - Genesis 4:13-16
Cain and Abel: Sarcastic Reply - Genesis 4:9
The Fall: Humanity Cursed - The Christian Worldview
The Fall: No Repentance - The Christian Worldview
How Bad Is Sin? (Part 2) - The Christian Worldview