CAIN THE HERO

Cain and Abel went out to the field. That's all the TORAH tells us. But they went to the field to have a discussion. Abel said, I have drawn a line in the sand. The world on your side of the line is yours and the world on my side of the line is mine. On my side, a great Temple to God will be built. On your side, idolators will rule. Abel said, on my side of the world, great gold and silver will be found. On yours, iron and brass. Abel said, we are now mature and desire for a woman besets us. As there is only one female in the world, our mother Eve, I will kill our father Adam and take our mother for my wife.

The insult to his mother was more than he could bear and he struck Abel to teach him to shut up. Unfortunately, the blow killed him.

God called out to Cain and asked him where Abel was.

Cain said, HASHOMER ACHI ANOCHI? Am I my brother's guardian?

God said, your brother's blood cries out to me.

Cain made an act of VIDUI, confession and atonement.

He said, MY sin is greater than I can live with. How can I ever be forgiven? Where ever I go, people will kill me for shedding his blood.

God said, I will place a sign on you that will show people not to harm you.

In the English speaking world, people called this "the mark of Cain"; the implication is that it is the sign of a murderer. But in Hebrew, the word is OT,  sign. Whenever this word is used in the TORAH, it is used positively.

EXODUS 3:12 AND HE SAID, "CERTAINLY I WILL BE WITH YOU, AND THIS SHALL BE THE SIGN TO YOU THAT IT IS I WHO HAVE SENT YOU: WHEN YOU HAVE BROUGHT THE PEOPLE OUT OF EGYPT, YOU SHALL WORSHIP GOD AT THIS MOUNTAIN."
GEN 4:15 THE LORD TOLD HIM, "THIS WON'T HAPPEN, BECAUSE WHOEVER KILLS YOU WILL SUFFER SEVEN TIMES THE VENGEANCE." THEN THE LORD PLACED A SIGN ON CAIN SO THAT NO ONE FINDING HIM WOULD KILL HIM.
GEN 9:13 I HAVE PLACED MY BOW IN THE CLOUDS, AND IT WILL BE A SIGN OF THE COVENANT BETWEEN ME AND THE EARTH.
GEN 17:11  YOU MUST CIRCUMCISE THE FLESH OF YOUR FORESKIN TO SERVE AS A SIGN OF THE COVENANT BETWEEN ME AND YOU.
GEN 48:20 SO HE GAVE THEM HIS BLESSING THAT DAY, SAYING, YOU WILL BE THE SIGN OF BLESSING IN ISRAEL, FOR THEY WILL SAY, MAY GOD MAKE YOU LIKE EPHRAIM AND MANASSEH
EXO 13:16 SO LET IT BE A SIGN ON YOUR HAND AND A SYMBOL ON YOUR FOREHEAD, FOR THE LORD BROUGHT US OUT OF EGYPT BY THE STRENGTH OF HIS HAND."
EXO 31:13 SPEAK THOU ALSO UNTO THE CHILDREN OF ISRAEL, SAYING, VERILY MY SABBATHS YE SHALL KEEP: FOR IT IS A SIGN BETWEEN ME AND YOU THROUGHOUT YOUR GENERATIONS; THAT YE MAY KNOW THAT I AM THE LORD THAT DOTH SANCTIFY YOU.
EXO 33:16 FOR IS NOT THE FACT OF YOUR GOING WITH US THE SIGN THAT I AND THIS PEOPLE HAVE GRACE IN YOUR EYES?

God gave Cain a sign of Divine Protection. Some said that the sign of Cain was circumcision.

Cain goes off and gets married and has a son whom he names Enoch; the name means teaching or instruction. He then builds the first city ever and calls the city Enoch, after his son. It is the city of instruction or learning. What was the first thing people noticed when they approached a city? The walls. We no longer have walled cities because walls can no longer protect us. But we are not that far removed from walled cities, maybe 200 or 300 years.

And on the walls, what? Guardians. Cain had asked God if he were his brother's guardians. But later in life, he provided guardians for anyone seeking refuge in his city if they came there to learn about the ways of God.

Finally, We know that Abel's death was an accident, not intentional by learning about the death of Cain. The TORAH teaches the principle of Measure for Measure. What you do to another will be done to you.

Genesis 4:18–24
To Enoch was born Irad, and Irad fathered Mehujael, and Mehujael fathered Methushael, and Methushael fathered Lamech. 19 And Lamech took two wives. The name of the one was Adah, and the name of the other Zillah.  Lamech said to his wives: "Adah and Zillah, hear my voice; you wives of Lamech, listen to what I say: I have killed a man for wounding me, a young man for striking me. If Cain´s revenge is sevenfold, then Lamech´s is seventy-sevenfold.’

A MIDRASH says that Lamech actually killed Cain inadvertently in a hunting accident. Thinking Cain was an animal, Lamech shot him. Another MIDRASH says

The Sages Parable
Lamech was a seventh generation descendant of Cain. He was blind, and he would go out hunting with his son, [Tuval-Kayin]. [His son] would lead him by the hand, and when he would see an animal, he would inform his father, [who would proceed to hunt it]. One day, [Tuval Kayin] cried out to his father: "I see something like an animal over there." Lemech pulled back on his bow and shot. ... The child peered from afar at the dead body... and said to Lamech: "What we killed bears the figure of a man, but it has a horn protruding from its forehead." Lamech then exclaimed in anguish: "Woe unto me! It is my ancestor, Cain!" and he clapped his hands together in grief. In doing so, though, he unintentionally struck Tuval-Kayin and killed him, too. (Tanchuma to Genesis, 11)

https://www.aish.com/jl/b/eb/ca/48950551.html