See: God Questions His Creation: Genesis 4:11-12 (b)
4:13 Cain said to the LORD, “My punishment is greater than I can bear. 14 Behold, thou hast driven me this day away from the ground; and from thy face I shall be hidden; and I shall be a fugitive and a wanderer on the earth, and whoever finds me will slay me.” 15 Then the LORD said to him, “Not so! If any one slays Cain, vengeance shall be taken on him sevenfold.” And the LORD put a mark on Cain, lest any who came upon him should kill him.
Now suddenly Cain shows some remorse. As is often the case with humans, it is not committing the sin which bothers us, it is getting caught. Our sorrow is often related to the consequence we suffer, rather than lamenting the suffering we inflict on others.
“My punishment is greater than I can bear…” In one sermon Chrysostom portrays Cain as trembling uncontrollably at this point in the story. St. John sees Cain’s punishment as being worse than death. “God wanted men of later times to exercise self-control. Therefore, he designed the kind of punishment that was capable of setting Cain free from his sin. If God had immediately destroyed him, Cain would have disappeared, his sin would have stayed concealed, and he would have remained unknown to men of later times. But as it is, God let him live a long time with that bodily tremor of his. The sight of Cain’ palsied limbs was a lesson for all he met. It served to teach all men and exhort them never to dare do what he had done, so that they might not suffer the same punishment. And Cain himself became a better man again. His trembling, his fear, the mental torment that never left him, his physical paralysis kept him, as it were, shackled. They kept him from leaping again to any other like deed of bold folly. They constantly reminded him of his former crime. Through them he achieved greater self-control in his soul.” (AGAINST JUDAIZING CHRISTIANS)
“…from thy face I shall be hidden…” Cain has a legitimate fear. He has been trying to hide his activities from God’s presence, but now is terrified to realize that in fact God might never look upon him with favor again. We all in Psalm 51:11 pray that God will not cast us away from His presence and that He will not take His Holy Spirit from us. Cain’s spiritual lesson is a difficult one. As with most of us, Cain does not want God observing his every word, deed and thought. He wants God to ignore him for most of what he does, especially that which is wrong. But when Cain wants God present, he expects God to be at his beck and call to rescue him and protect him.
“…a fugitive and a wanderer on the earth…” The implication of the text is that Cain will never be able to be a citizen of any civilized people. He has in fact cut himself off from society.
Chrysostom comments that just as Cain’s repentance came too late – only after the punishment was ordered – so too those who fail to repent before the Judgment Day will be sorely disappointed when they attempt to repent after God has pronounced judgment. Yes they will at that moment be sincerely sorry for their sins, but no it will not save them from eternal punishment. It is not the sorrow that saves, but changing one’s life while there is still time. God promises to accept our repentance and promises to forgive our sins. He does not however promise us a tomorrow. Now is the time of salvation (2 Corinthians 6:2).
God puts a mark on Cain to protect him so that no one kills him. Why didn’t God so mark Abel whose sacrifice was pleasing to Him?
God does not immediately requite the death of Abel by slaying Cain. Why? Perhaps to give Cain the chance to repent. “Therefore I will judge you, O house of Israel, every one according to his ways, says the Lord GOD. Repent and turn from all your transgressions, lest iniquity be your ruin. Cast away from you all the transgressions which you have committed against me, and get yourselves a new heart and a new spirit! Why will you die, O house of Israel? For I have no pleasure in the death of any one, says the Lord GOD; so turn, and live” (Ezekiel 18:30-32). God is not demanding retributive justice, but rather hopes for the conversion of the sinner.
Another theme of warning from Great Lent – humans are capable of being deceived. We need to learn a certain wisdom – a holy skepticism about our own desires, wants, cravings, perceived needs. We must learn discernment. Just because something looks good or feels good or seems pleasurable, does not mean it has goodness in itself (See Genesis 3:6 – “So when the woman saw that the tree was good for food, and that it was a delight to the eyes, and that the tree was to be desired to make one wise, she took of its fruit and ate; and she also gave some to her husband, who was with her, and he ate.”) The warning of the hymn is to us – it doesn’t do Adam any good and cannot change what happened in the past. “Adam” is long dead, but we the children of the first human can learn the lesson – Adam’s story is our story and is about us. Treating Genesis 2-3 as purely literal history lessons empties them of their value to the sons and daughters of Adam who still live on the same earth he did – namely us! We learn the story of Adam and Eve, not to regret the sins of our ancestors, but in order ourselves to avoid sin and to embrace the life in God. It is we who have to learn how to live on this earth in a godly fashion – the story is of no value to the first humans, Adam and Eve! 
Fraternized 