What are the connotations of "Lachein Kol Horeig Kayin" and "Shiv'asayim Yukam"?
Rashi: "Lachein Kol Horeig Kayin" is a warning aginst killing Kayin, 1 and the Torah is hinting that anyone who dares to kill Kayin will be punished 2 - because Hashem only intends to avenge the death of Hevel after seven generations.
Ramban: It means that whoever kills Kayin will be punished sevenfold.
Da'as Zekenim and Targum Onkelos: It means that whoever kills Kayin will receive his punishment seven generations later.
See Sifsei Chachamim.
Rashi: Without sactually saying so - Like we find in Shmuel II 5:8, and in Divrei Hayamim I 11:6.
According to Rashi, the Torah writes, "Therefore whoever kills Kayin...!" - and leaves the punishment unsaid?
Rashi: It is normal for the Torah to do this. 1
See for example, Shemos 22:22. It is like saying to someone, 'Don't you dare do that, or else ...!'
What sort of sign did Hashem give Kayin as a protection?
Rashi and Targum Yonasan: Hashem imprinted a letter of His Holy Name on Kayin's forehead, so that whoever saw it would be afraid to cause him harm. 1
Ramban #1: It was some sort of sign that indicated to Kayin where he was to travel - so that he knew that it was safe to travel in that direction.
Ramban #2 (citing the Midrash): The sign of protection against the Chayos was a dog, which not only protected him against other Chayos, but went ahead of him and he followed, knowing that wherever the dog led him it was safe for him to go.
Oznayim la'Torah (citing the Tanchuma): It was in the form of two horns - which explains why Tuval Kayin though it was a Chayah that he saw.
Gur Aryeh: The Pasuk does not specify what the "Os" was. It is most likely that "Os" would mean "a letter," which would show that Hashem did not wish that Kayin be killed [at this time].
Why was Kayin killed in the end? Exile should have atoned for him!
Moshav Zekenim: Exile atones only for Shogeg. However, it did help to delay his death.
QUESTIONS ON RASHI
Rashi writes: "'Whoever kills Kayin...!' - an unspecified threat." Why does Rashi explain this way?
Gur Aryeh: The following phrase, "shall be avenged [after] seven [generations]," means that Hevel will be avenged, through Kayin's death. It cannot be a continuation of, "Whoever kills Kayin." Rather, the opening phrase of the Pasuk is a threat left open.
Rashi writes: "... And the end of the verse proves it." Why not interpret the verse simply; 'Whoever kills Kayin shall [himself] receive his vengeance after seven generations'?
Gur Aryeh: Kayin received a reprieve of seven generations due to his request in the preceding verse (4:14); but why would he who kills Kayin receive such a reprieve? 1 [I.e. each person can only earn it through his own prayer or merit.]
Gur Aryeh: We also should not translate as, 'Whoever kills Kayin will receive vengeance sevenfold,' for that would not be just.
