Just getting back to this article… I appreciate the sharing of dialogues you’re having. Dialogue is an excellent way to learn and grow (so I’m finding). 

You asked:

“Wouldn’t you agree that our God was full of grace toward Cain when God stated the truth to him in Gen 4:7?”
>>> Yes, the grace of God is so obvious. Yet I missed it every time I studied this passage :(  Probably I missed seeing grace in the Genesis passages because I typically studied the Bible in order to validate or prove my ideas and justify my life choices. Now that I study the Bible to learn the meaning of the text, I see grace abounding.

“Isn’t the gracious God of angry Cain also the gracious God of the wayward younger son and the gracious God of the Pharisee-like older son (Lk 15:11-32)?”
>>> Yes, He is the same Lord. It is significant to me that the NT speaks of “grace” (charis) while the OT speaks of “graciousness” (chen). I also firmly believe that grace is the unshakeable foundation of Christianity. The graciousness presented in the OT points to Jesus, the grace revealed in the NT.

“Shouldn’t grace (not just truth in our words) color all we do as Christians?”
>>> Yes, grace (in my study so far) is the stabilizer of what we do as Christians. If we are not centered on the grace of our Lord Jesus, we are clearly off-center in our teaching and our actions, and if we are honest, we can easily see the fruit of not being centered on grace.

As to your friend’s questions:

“How do you teach Genesis 4:7?”
>>> I would answer: The same way you teach any verse in the Bible. First you pray. Then you learn the meaning the author intended. Then you read what the great theologians have said about that verse throughout history. Then you pray some more. Then, finally, you learn what those you are teaching have to say about it. And specifically in regard to Genesis 4:7, we must not take that verse out by itself or it may easily loses its intended meaning. 

“Didn’t God press upon Cain to ‘do what is right’?”
>>> Genesis 4:6,7 reads “6 Then the LORD said to Cain, “Why are you angry? Why is your face downcast?  7 If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must master it.” Our Lord said this to Cain, whose offering had just been reject by the Lord. Cain was angry and downcast. In light of this, 4:7 is a word of grace to Cain. What “right thing” did our Lord want Cain to do? It was to make an offering out of love for the Lord, as an act of worship, not as an act of duty. 

“Shouldn’t we help our Bible students to ‘do what is right’?”
>>> No, we should not. This is a vague question. Who defines what “is right”? The Bible is not a book of morality, but a book of relationship. No one has a right to define “what is right” apart from Scripture. We are dangerous teachers who deserve every woe of Jesus if we bind our Bible student’s consciences to a set of rules and practices, claiming those practices are the best way or the only way to grow as a disciple of Jesus. 

“Or should we just extend grace to them, and let them do whatever they want?”
>>> This question shows me the person asking it has little idea what the grace of God is about. These questions reveal a thought pattern that defines grace as “letting people do whatever they want”. That is not the grace Scripture speaks of. Grace is something we are bound to when we believe. Grace holds us accountable and grace rules our actions, our thoughts, our hearts. The grace of God is not a license for immorality as Jude 1:4 states clearly: “For certain men whose condemnation was written about long ago have secretly slipped in among you. They are godless men, who change the grace of our God into a license for immorality and deny Jesus Christ our only Sovereign and Lord.”

When I teach Gen 4:7 I always assumed that if that verse is true, then the reverse should be true, that in fact the best way to get mastery over sin and avoid sin being on your doorstep is to do what is right. I’ve struggled with addiction and found that the number one best way to avoid temptation is to be doing what you should be doing. I find it very interesting in the Bible that sin and temptation is described as something we “fall” into, like a pit we carelessly stumble upon. It’s only possible if you’re totally not paying attention or don’t care where you are going–I mean who falls into a pit? By the time God counseled Cain he was already beyond the point of no return, he was a path. Mk 4:15 As was the case with Eve, she created an environment for Satan to come in and was already lost by the time Satan came to her because she wasn’t doing what she should have been doing. When we look at Cain, I’m always amazed by the ridiculous amount of grace given to him in Gen 4:15. The mark of grace given I often say must have been the mark of the cross on his forehead. Yet, this grace had absolutely zero effect on Cain who passed on a ideology of cheap grace that exponentially corrupted his descendants until the entire world became more depraved than any time in history and robbed the identity of every single believer on the planet except one. Like the people in Paul’s time they used grace as a justification for their wickedness. Rom 6:1 However, while God was merciful for a time, his wrath is clearly revealed against the wickedness of men Rom 1:18 and surely at some point Cain’s rejection of God sent him to hell. Even if God is full of grace the fact is there is judgement, even if we claim God is full of grace we can’t deny that he throws people to hell. 

I believe that teaching people “do what is right” is a passionate attempt to help them flee from the coming wrath. Mt 3:7 Spurgeon wrote: “I have no doubt that the Pharisees and Sadducees were very surprised to hear John addressing them in that way; for men who wish to win disciples, ordinarily adopt milder language than that, and choose more attractive themes, for they fear that they will drive their listeners away if they are too personal, and speak too harshly. There is not much danger of that nowadays, for the current thinking today is that gospel ministers instead of piercing men and women with the sword of the Spirit, only show them only its handle; they let them see the bright diamonds on the scabbard, but never let them feel the sharpness of the two-edged blade. They always comfort, and console, and cheer, but never allude to the terrors of the Lord.”

The conflict I have though is that I know many who tried to tell their kids “do what is right” only drove them away. Yet, those who bore with their children, found that when they let them go they came back. It is like the father of Lk 15 who seems to not care what will happen to his son and “gives in”. Yet, in fact he knew the full depth of what would happen and prayed, straining his eyes to the horizon waiting for his son to return. It’s really a complicated issue. Skirting the line between grace and truth, seems to raise more questions than it solves. :)