What sort of book is the Torah referring to here?
Rashi and Targum Yonasan: It is not a book to which the Torah is referring ('Seifer' in Biblical times actually meant a scroll), but a list of Adam's offspring (from the word 'Sefirah' - counting or relating) that the Parshah now presents. 1
Ramban #1: It means literally a book, and it refers to the entire Torah, which describes what happened to Adam's offspring. 2
Ramban #2 (in 5:2): Adam refers, not just to Adam ha'Rishon, but to the whole of Mankind. 3
Seforno: Refer to answer #1 - only 'Toldos' refers, not just to Adam's offspring (mankind), but what happened to them. 4
Avodah Zarah 5a: Hashem showed Adam the Chachamim and leaders of all generations. 5
According to the Ramban's understanding of Rashi.
Moshav Zekenim: It teaches that Torah should have been given through Adam; but since he was not able to keep one Mitzvah, surely he could not keep 613!
See Rashi and Seforno to Bereishis 37:2.
Maharal (Tif'eres Yisrael Ch. 47, p. 145): Adam ha'Rishon was the root from which of all of mankind emerged; all future people and events were included in him. See also Oznayim la'Torah, end of DH 'Zeh Seifer', #2 & #3, who elaborates; as well as Torah Temimah, note 1.
Why does the Torah need to mention here that He created Adam in the Divine image - a fact that it already mentioned earlier - in Bereishis 1:26?
Ramban: To teach us that not only was Adam created from nothing, but so was Chavah.
Seforno: To teach us that He created him with freewill and choice, which explains why, whenever he and his offspring sinned, they were punished.
Yerushalmi Nedarim, 9:4: To teach us to respect another Jew, because he is created in the Divine Image - which takes priority over the well-known principle "v'Ahavta le'Re'acha Kamocha", 1 since the latter permits one Jew to do to another in any manner that he would not object others doing to him.
Which R. Akiva described as 'K'lal Gadol ba'Torah'.
QUESTIONS ON RASHI
Rashi writes: "'On the day of Hashem's creating'... - This teaches us that on the same day that Adam was created, he had children". But perhaps the verse means, "On the day that G-d created man, He made him in the semblance of G-d", or, " ... He created them male and female"?
Mizrachi: If so, the phrase, "'On the day of Hashem's creating" could be omitted. Was man in the Divine image only on that first day, and not afterwards?
Gur Aryeh: It is obvious that the Divine image of man, and being male and female, were inherent in man from the day of his creation, and could not have come afterwards. The only possible lesson to derive from this phrase is, "... the offspring of Adam [came] on the day he was created."
