The story that the medrash tells us about Lemech killing his ancestor Cain and his child Tuval Cain is, indeed, tragic. It brings up deep questions about Divine Justice. According to the Rabbis, Lemech was blind. He was out hunting with bow and arrow, accompanied by his third son, Tuval Cain, who was his "eyes". At one point, Tuval Cain sees what appeared to be an animal, and helped his father aim and shoot. When they discover that it was, indeed, Cain they had killed, Lemech claps his hands together in grief, accidentally killing (I guess by a blow to the head) Tuval Cain.
What does this story mean? Where was God's protection of Cain? Further, why did Lemech deserve to be the accidental victim of this tragedy? In truth, I believe that Lemech was not such an accidental killer, in a larger sense. The death of his ancestor and his son was not unrelated. In fact, one could say that Lemech killed his son before he killed him, and by so doing, he killed Cain forever. How so?
Think about it. Cain was now the father of all mankind. Abel died without offspring. The future of the human race is Cain's and it hinges on his sincere repentance for the act of murder he committed. Cain has, indeed, repented of the deed, but whether he has repented of the mindset that lead to the deed remained an open question. I suggest that it only became clear when the result of Cain's parenting and education of his children became visible in Lemech. What did Lemech do?
A couple of things. The Torah tells us about the careers of Lemech's three sons. Jabal was a shepherd. Jubal was a musician. Tuval Cain was a welder and blacksmith. According to Ramban, the great medieval commentator, Tuval Cain manufactured swords and spears, tools of violence. All three sons were taught their professions by Lemech. Thus, the first mistake of Lemech was in training his son to make these terrible things. The second was that he, himself, was a hunter. At this time in history, mankind was to be vegetarian.
Why would Lemech teach Tuval Caim armament manufacture? He would echo the gun lobby by saying that people kill, not weapons. By why make weapons in the first place? Perhaps he was afraid of others, and wanted to be able to defend himself. If so, that is the clear repudiation of Cain's repentence. Cain had been assured by God of a sign that would protect him. Cain had no need to arm himself. Indeed, Cain was ecstatic with his forgiveness. He finally found the Good Life. But not so Lemech.
In the Torah, there are two sections of Curses, one in Leviticus, and the other in Deuteronomy. They are both preceded by short sections of blessings and reward. "If you follow in my ways.." a number of wonderful things will happen. But if not, then a very long and fearful list of consequences follows. Now, according to the Talmud, God's attribute of kindness is greater than His Wrath. If so, then, I would expect the blessings to be much more plentiful than the curses.
In truth, I believe they are. The Curses, while certainly longer in text, are a list of details and specifics. The blessings, while shorter, are more global. A person who sees the world through negative lenses will find a thousand reasons to suffer. A person who sees and seeks the good will live in a world filled with light, flowers and music.
When a person begins to think of possibilities, they open up to them. The question of life is what possibilities one sees. Lemech saw a world of dangerous possibilities, that people could turn on him, that there were killers in potential. Further, by being a hunter, he himself had opened himself to killing. According to Jewish tradition, a shochet (kosher butcher) should also be cantor. Since he works in a cruel field, he should compensate by asking mercy for the people.
So when Lemech taught his son to make swords, he showed that Cain's repentance did not develop completely. The mindset that ignited his fratricidal jealousy was still influencing his descendents. Thus, since his repentance wasn't complete, his punishment now came at the hands of his descendent. And Tuval Cain was Lemech's victim too, by introducing him to this bleak mindset and influencing him to make tools of war.
When Adam and Eve saw what had become of the Cain lineage, they realized that the world would become a very bad place to live in. They took the only course they could to correct things, and had another son, Seth. Through him, humanity would have a better chance.
So this is the power of positive thinking, of what we choose to look at. Do we see the beauty in life, the wonders of nature, the glory of God? If so, weapons, jealousy, violence have no place in our heart and in our world. If we see the problems, the faults, the dangers, the they will be plentiful and they will be exaggerated. Even small things, like a brother succeeding where we failed, will become terrible sufferings for us.
The choice is ours. It starts with what we choose to look at in this world, to think about, to spend our time and energy on. If we choose to relive, in our minds, our achievements, the highlights of our days, we will be positive people, and our life will be The Good Life.