Genesis 4:23

And Lemek said to his wives Ada and Zillah, Hear my voice, wives of Lemek, hearken to my words: for I have not killed a man, that I should be slain for him; neither have I destroyed a young man, on whose account my children should perish.

AND LAMECH SAID UNTO HIS WIVES. For the sense of this verse, the commentators have depended on the opinion of Onkelos who explained therefore whosoever slayeth Cain vengeance shall be taken on him ‘shivatha’im’ as meaning that at the end of seven generations, vengeance shall be taken on him [Cain], but not now because G-d would be long-suffering with him. Now Lamech’s wives feared to bear children because they would be the seventh generation to Cain, but he comforted his wives by saying that G-d would be forbearing with him for yet seventy-seven generations because he would pray before Him, for He is long-suffering and would have mercy upon him. Or it may be that Lamech’s words were an absurd a fortiori argument, in accordance with the Midrash that Rashi mentioned, [namely: “For if so, the Holy One, blessed be He, could never exact His debt nor fulfill His word.”] If so, Scripture is stating: “Therefore whosoever slayeth Cain, vengeance shall be taken of the seventh generation” and not in his days. And this is the translation of Onkelos: “All who would slay Cain! In seven generations, punishment will be exacted of him [Cain].” But if so, it would have been proper that the verse, And Lamech said unto his wives, appear before [Verse 20: And Adah — Lamech’s wife — bore Jabal].
In my opinion, the word shivatha’im does not mean “seven generations” because this word is not used for seven separate units but rather for the multiplying of one thing seven times, such as: refined ‘shivatha’im’ (sevenfold); restore ‘shivatha’im’ (sevenfold); and the light of the sun shall be ‘shivatha’im’, meaning doubled and redoubled seven times. But the meaning of therefore, whosoever slayeth Cain is, according to its real sense, that G-d said: “Therefore, whosoever slayeth Cain will have vengeance taken on him sevenfold, for I will punish his slayer seven times for his sin, since I have promised Cain that he will not be slain in view of his fear of Me and his confession before Me.” However, the matter of Lamech and his wives is not mentioned clearly in Scripture. We could also say that they feared lest Lamech be killed as a punishment for his ancestor’s sin since G-d did not tell Cain, “I have forgiven you.” Instead, He promised him only that he will not be slain, but He would collect His debt from his children, and they did not know when. And so indeed the matter happened. Lamech, however, comforted them by …

שמען קולי נשי למך, Lemech called out in grief

אמרתי, I have to express my mental anguish’

הרגתי לפצעי, I have caused myself real injury, for the one who has killed my father (ancestor Kayin) has inflicted upon me the child a deep wound, seeing that the killer was my son.

ויאמר למך לנשיו, our sages in Bereshit Rabbah 23,4 state that when Lemech wanted to sleep with his wives they refused him. They used several arguments, one being that they were afraid of the deluge and they did not want to give birth to children already doomed. Lemech countered that if Kayin whose deed of foul murder had resulted in suspension of his death sentence for 7 generations, then he, Lemech, who had killed inadvertently, accidentally, would not be punished for far longer than that, and his wives had no reason to worry. Even if a deluge would come tomorrow, he was free from the taint of sin and would not become its victim. He went further, saying that even assuming he had deliberately killed a man or a child, G’d would forgive him, seeing he had many merits which would offset one such sin. Kayin had not had such merits even before he killed his brother but had sinned so that G’d had rejected his offering, and still his sentence had not been carried out for seven generations. This is how he arrived at the expression שבעה ושבעים as opposed to שבעתים the period during which G’d had suspended the carrying out of the sentence of death on Kayin. He appealed to G’d’s patience to extend this patience to him. It is also possible that Lemech’s logic was totally foolish, as hinted at by Rashi, as the wives of Lemech did not worry about retribution for Lemech’s sin but the long overdue retribution for Kayin’s sin, something that would include all of Kayin’s offspring. We have to assume that Lemech’s speech to his wives took place before his wife Adah had given birth to Yaval.
Some of our sages (Tanchuma 11), claim that Lemech was blind and that when whenever he went out hunting a child (Tuval Kayin) would serve as his guide. When the child spotted the animal he would tell Lemech to draw his bow and aim his arrow in a certain direction. In this fashion Kayin, while being mistaken for an animal, was killed. Other sages (Bereshit Rabbah 22,12) claim that the “sign” provided by G’d for Kayin to warn people and beasts not to kill him, was a horn which grew out of his forehead. Kayin, being constantly on the move in the field due to G’d’s curse, was mistaken by the boy accompanying Lemech for a wild beast seeing that it had a horn on its forehead. Once the boy and Lemech came close to inspect the “beast” they thought they had killed, the boy told Lemech that they had killed a human being. Lemech then suddenly realised that he had killed his ancestor Kayin and …