Adam and Eve could not even keep the simple commandment that He gave in its letter. I want you to notice: He informed. They sinned. And He judged. There is the pattern. God always follows that pattern. He always informs people. As we are going to see, even the heathen are informed. Those He has called into His own church are informed better than anybody else, but everybody on earth is informed enough for God to judge.
From these verses it is very clear that they were instructed regarding the offerings. Abel simply followed God's instructions. Cain did not. Look at verse 7 again, and then we are going to look at verse 13 because we want to see Cain's reaction.
How can good and bad be judged unless He instructed them? They knew what was good. They knew what was bad. Abel did what was good, but Cain, like his mother before him, shifted gears a little bit and substituted his own thinking regarding what would be acceptable to God. Verse 13 gives Cain's reaction. He was angry.
Again, God informed. Cain disobeyed. God judged. The pattern is followed. So it was Cain then, representing mankind, who was unjustly angry at God's judgment. In his eyes, he had become victimized by God. Thus we already see two patterns developing. First, God lets mankind know what He expects. His expectation is not even to the level of the New Covenant. At most it is the level of the Old Covenant. Secondly, mankind disobeys, and then feels unjustly treated in God's judgment.
Cain fell victim to this all-or-nothing thinking distortion.
It was not a matter of Daddy or Momma likes my brother more than me. It was a matter of variable conditions over which Cain did have some control. As John Ritenbaugh stated on Trumpets, Cain knew the preconditions. There was a wide spectrum of choices Cain could use, rather than the simple, He likes me/He does not like me.