Why does the Torah interrupt the dialogue between Lavan and Yaakov with a description of Lavan's daughters?
Rashbam: To explain why of Lavan's two daughters, Yaakov 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 Yaakov offered to work for seven years. Why would three years not suffice? "Tov Titi Osah Lach..."! (a) Yaakov feared lest Lavan insist that Yaakov marry both daughters, and Yaakov did not want to; (b) Lavan might say that he does not want to give the younger before the older, or Yaakov must wait until Leah marries; (c) Leah's eyes were soft - Lavan would use every strategy to get Yaakov to marry the daughter with a shortcoming; (d) Rachel was beautiful, and Lavan would want much for her. 2
In spite of the fact that, already from their first encounter at the well, it seems that Yaakov knew that he would marry Rachel (Refer to 29:11:2:1).
Malbim (18): Yaakov 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 Yaakov worked for Lavan during that period - since no mention of it was made until now?
Ramban #1: It seems that, from the moment he encountered Rachel by the well, where the Torah records, "he watered Lavan's sheep" (29:10), he continued to do so, to spare Rachel, whom he loved, the onus of doing so.
Ramban #2: Yaakov 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 - not for nothing of course....
What does Lavan mean by, "Ha'Chi Achi Atah, va'Avadtani Chinam"?
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 - crafty like you. Do I think that you work for me for free?! Surely, later you will claim what is proper for you according to law! Therefore, I ask you to state your wage. Refer to 29:15:152:1 and 29:15:152:2 and the note there.
Malbim: A worker who did not stipulate about the wage, he is paid based on the local custom. However, there is no custom for one who works for his brother. Later you can claim wages without limit!
Lavan craved money, even through theft. He is not concerned for "v'Sonei Matanos Yichyeh" (Mishlei 15:27). He should be thrilled that Yaakov work for him for free!
Tosfos ha'Shalem (5, citing R. Efrayim):Lavan knew that a Shomer Chinam is exempt. He preferred to pay Yaakov a little, to obligate him for what is stolen or lost.
Ohr ha'Chayim 1 : Lavan came to decrease Yaakov'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 Yaakov 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 Metzia 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 Yaakov later demand according to the custom. (PF)