Why does the Torah interrupt the dialogue between Lavan and Yakov with a description of Lavan's daughters?
Rashbam: To explain why of Lavan's two daughters, Yakov wanted the younger one. 1
Ohr ha'Chayim: It teaches why there was no way for Lavan to give Leah in place of Rachel. Refer to 29:16:152:2 and the note there.
Malbim (16,17): It explains four reasons why Yakov offered to work for seven years. Why would three years not suffice? "Tov Titi Osah Lach
In spite of the fact that, already from their first encounter at the well, it seems that Yakov knew that he would marry Rachel (Refer to 29:11:2:1).
Malbim (18): Yakov estimated that three years suffice for a beauty like Rachel. He added two years, lest Lavan insist that he marry also Leah, and another two, lest Lavan might say that he does not want to give the younger before the older.
How do we know that Yakov worked for Lavan during that period
Seforno: Refer to 29:14:1:1*
Ramban #1: It seems that, from the moment he encountered Rachel by the well, where the Torah records (in Pasuk 10) "and he watered Lavan's sheep", he continued to do so, to spare Rachel, whom he loved, the onus of doing so.
Ramban #2: Yakov initially stayed with him as a guest. However, after a month passed and Lavan saw that he was living off his kindness, he tricked him into working for him by flattering him. He told him that the man of ethics that he was, he would never agree to live off somebody else. He would therefore be bound to volunteer to work for him
What does it mean "Hachi Achi Atah va'Avadtani Chinam"?
Tosfos ha'Shalem (1, citing R. Efrayim): It is proper that you work for me for free, for we are brothers. However, I do not want this. Refer to 29:15:152:1,2.
Bechor Shor: Since we are brothers, it is a greater evil if I do not pay you properly.
Ohr ha'Chayim: I am your brother
Lavan craved money, even through theft. He is not concerned for "v'Sonei Matanos Yichyeh" (Mishlei 15:27). He should be thrilled that Yakov work for him for free!
Tosfos ha'Shalem (5, citing R. Efrayim):Lavan knew that a Shomer Chinam is exempt. He preferred to pay Yakov a little, to obligate him for what is stolen or lost.
Ohr ha'Chayim 1 : Lavan came to decrease Yakov's wage. The Rambam (Hilchos Sheluchim 8:2,3) writes that if they did not stipulate, the shepherd gets half the increase. Lavan was concerned, for Yakov had told him 'I am crafty to get what I need' (refer to 29:13:3:5).
Refer to 29:15:151:4.
Based on Hagahas Ohr Yakar (also below, 30:41), in Likutei Ha'aros on Ohr ha'Chayim. Ba'al ha'Ma'or (Bava Metzi'a 39b) says that the wage is based on the standard custom. Even if the shepherd's portion was different then in Aram, Lavan feared lest Yakov later demand according to the custom. (PF)