Genesis 4:8 Cain said to Abel, his brother, “Let’s go into the field.” It happened when they were in the field, that Cain rose up against Abel, his brother, and killed him. 9 Then God said to Cain, “Where is Abel, your brother?” He said, “I do not know. Am I my brother’s keeper?” 10 And God said, “What have you done? The voice of your brother’s blood cries out to me from the ground. 11 Now you are cursed because of the ground, which has opened its mouth to receive your brother’s blood from your hand. 12From now on, when you till the ground, it won’t yield its strength to you. You shall be a fugitive and a wanderer in the earth.” 13 Cain said to God, “My punishment is greater than I can bear. 14 Look, you have driven me out this day from the surface of the ground. I will be hidden from your face, and I will be a fugitive and a wanderer in the earth. It will happen that whoever finds me will kill me.” 15 The LORD said to him, “Not so. Whoever kills Cain vengeance will be taken on him sevenfold.” The LORD appointed a sign for Cain, lest any finding him should strike him. NHEB
Even though they are now east of Eden, God is still speaking with them. As to Cain’s act, the question is whether this was a premeditated murder or does it just happen? Details are kept to a minimum as the actual killing is not the main point of the story. There are parallels to the Adam and Eve story as God shows up here and asks Cain “where is Abel”? This suggests to some that God is somehow ignorant but like Adam and Eve after they have eaten the fruit, God already knows the answer as demonstrated starting in verse 10. Cain’s first impulse is to lie.
In Genesis 4:7, Cain is standing at the edge of a precipice faced with a choice. He makes the wrong choice and faces curses similar to Adam and Eve. The word translated as “punishment” (Strong’s 5771) can also mean “sin” or “iniquity” and is typically translated as such, rather than “punishment”. This presents an interpretive dilemma: does Cain regret the killing or does he regret the punishment for that killing?
Genesis 4:13 And Cain said to the Lord: My iniquity is greater than that I may deserve pardon. Douay-Rheims
Genesis 4:13 And Cain said to the Lord God, My crime is too great for me to be forgiven. Brenton Septuagint
If we substitute “sin” or “iniquity” for punishment then the argument can be made that this is a plea for mercy as Cain is afraid that his sin is too great to be forgiven and as a result, he will be permanently set apart from God. If we fast forward, Cain is prosperous later in life and the mark God places on him in verse 15 is certainly a sign of grace. (Recall the old saying: Mercy is God not giving us what we deserve; grace is God giving us something we do not deserve). Rather than striking him down, perhaps God, in His infinite patience, is allowing some time for Cain to come to repentance.
2Peter 3:9 The Lord is not slow concerning his promise, as some count slowness; but is patient toward you, not wishing that any should perish, but that all should come to repentance. NHEB
Romans 2:4 Or do you disregard the riches of His kindness, tolerance, and patience, not realizing that God’s kindness leads you to repentance? BSB
With that said, the overwhelming majority of modern Biblical texts use “punishment” indicating that Cain’s regrets arise from being caught. The argument here is that Cain’s response is to complain about the severity of his punishment rather than show remorse for what he is done (not to mention the lying). While you can’t read tone in the text, his response to God’s question about not being his brother’s keeper sounds a little snide to many. John Calvin explains it thusly:
Nearly all commentators agree that this is the language of desperation; because Cain, confounded by the judgment of God, had no remaining hope of pardon. And this, indeed, is true, that the reprobate are never conscious of their evils, till a ruin, from which they cannot escape, overtakes them;….. this is the due reward of his late repentance that he feels a horrible torment for which there is no remedy, https://www.studylight.org/commentary/genesis/4-13.html
Perhaps it is a little of both for Cain. He has regrets for his actions but at the same time, is distressed about the consequences he must bear as a result of his sin. Cain’s comment to God about not being his brother’s keeper should gnaw at us as it goes against what we believe, and try to practice, as Christians. (All the more difficult for us to practice these days in a world that is increasingly antagonistic toward Christians).
Philippians 2:3 Do nothing out of selfish ambition or empty pride, but in humility consider others more important than yourselves. 4 Each of you should look not only to your own interests, but also to the interests of others. BSB
Galatians 5:14 For the whole law is fulfilled in one word, in this: “You are to love your neighbor as yourself.” 15 But if you bite and devour one another, be careful that you do not consume one another. NHEB
This world is only going to work if we are concerned about others and they are concerned about us. If not, then like Cain, sin is crouching at our door. It starts easily enough as pride or jealousy and grows from there into anger and then into hate. The more it grows, the harder it becomes to repent of it. In the Sermon on the Mount, Jesus talks about the commandment not to commit murder but extends this to insulting a brother, as well. The word He uses in Matthew 5:22 (and often used without translation in many texts) is “Raca” which describes the action of clearing your sinus and then spitting it out. If you regard someone with this type of contempt, you have sinned and are in danger. Bottom line is don’t be a Cain (or if you are, stop it)! This same teaching can be found in the Old Testament:
Psalm 133:1 See how good and how pleasant it is for brothers to live together in unity. 2 It is like the precious oil on the head, that ran down on the beard, even Aaron’s beard; that came down on the edge of his robes; 3 like the dew of Hermon, that comes down on the hills of Zion: for there the LORD gives the blessing, even life forevermore. NHEB
Psalms 120-134 are the Psalms of Ascent that were often sung in the synagogues but also on the way to Jerusalem for the three trips made each year by the faithful. If these psalms were sung progressively, they would now be nearing the gates of Jerusalem and singing this song as they enter. This is a God thing – brothers in unity. There are two analogies here. The reference to Aaron and the anointing oil is a sign of the Holy Spirit. Second is the dew of Hermon. The Sea of Galilee has an outlet (the Jordan River) that is always draining to the Dead Sea which has no outlet. In that environment, how is it that the Sea of Galilee is always full? It has a source that keeps it constantly replenished. That would be Mount Hermon which is always covered in snow (imagine that!) . While the Bible never names the location, there are some who will make the case that Mount Hermon was the site of the Transfiguration.