Question: Doesn't the story of Cain and Abel defeat Calvinism? "The LORD said to Cain, “Why are you angry, and why has your face fallen? If you do well, will you not be accepted? And if you do not do well, sin is crouching at the door. Its desire is for you, but you must rule over it.”" -Genesis 4:6-7 (ESV) See God tells him if he does something he will be accepted.
Response: "If you do well" is a phrase with a verb in the subjunctive mood - a conditional statement which asserts nothing indicatively. "if you are willing", "if you hear", "if you do" declare, not man's ability, but his duty - what he OUGHT to do but such statements say nothing of what he CAN do.
While it is true that if Cain did well he would be accepted and that he had a duty to resist sin. But that doesn't mean that he had the moral ability to do so.
The passage also contains the command, "...you must rule over it." What does the Bible teach about the purpose of Divine commands? According to Paul in Romans 3:19-20, the purpose of imperatives (commands) are to reveal sin, man's inability, and NOT his ability to do what he is commanded. It reveals his impotence and desperate need of grace. This is the reason the Bible ITSELF gives for God commanding us to do things we we are incapable of doing. Therefore any other conclusion is man extrapolating using only his own human reason to conclude that we must have the ability if God commands it. In this case human reason directly contradicts God's word.
So God commanded Cain to do something he was unable to do and the whole time God knew he couldn't do it?