Why did Rachel and Leah say "due to these reasons, we should follow Hashem's command"? And why did Yaakov need to give reasons?
Seforno (to 31:14,16): They explained that it is not hard for them to leave, and that he should obey Hashem's command and leave immediately, without asking permission from their father.
Lev Eliyahu (Bereishis, p. 112): One should not think that he must suffer here to serve Hashem, and then the world to come will be nice. Rather, he should see that Avodas Hashem is best for him also in this world!
What does "Hitzil" mean?
Ohr ha'Chayim: It refers to recovering from a thief. He took our property (and Hashem returned it).
Why did they say "ul'Vaneinu"?
Ha'amek Davar: What should have been ours, Hashem gave to you. There is no difference, for in any case, after [we die] it will be to our sons. There were not concerned lest Yaakov marry another wife and father more sons (like Lavan suspected, and made Yaakov swear - 31:50), for they knew that a Tzadik would not marry from Benos Kena'an. 1
He should say that they knew that Yaakov will have 12 sons through four wives (Rashi to 29:34)! If not, Yaakov could find a wife elsewhere; Ramban (to 38:2) says that Yaakov's sons married girls from Mitzrayim, Amon, Mo'av, Yishmael and Bnei Keturah! Also, had Rachel received from Lavan, her [one or two] son(s) would get her entire share. Now, most of it will go to Yaakov's 10 other sons! (PF)
QUESTIONS ON RASHI
Rashi writes: "'Ki Kol ha'Osher' - The word 'Ki' in this context means 'rather.'" Why explain this way?
Gur Aryeh: It cannot mean 'because;' it is not giving a reason for the preceding statements. 1 The verses mean, 'Our father will never give us anything [willingly]; rather, the wealth that Hashem has taken away from him shall be our portion.'
I.e. Hashem's removing Lavan's wealth, in favor of Rachel, Leah, and their children, was not the reason that Lavan treated them as strangers.