What are the implications of "Lema'an Yirbu Yemeichem ... "?
Ramban #1: It comes to teach us that, although one is obligated to observe the Mitzvos even in Chutz la'Aretz when we are in Galus, the main Mitzvah is to observe them in Eretz Yisrael.
Ramban #2: It is coming to inform us that we will return from Galus and remain forever in Eretz Yisrael.
What is the meaning of "ki'Yemei ha'Shamayim al ha'Aretz"?
Ramban: It either means for all generations or it refers to 'the original heaven and earth at the time of the creation and the days of the world'. 1
Rashbam: It means that that the rain will descend from the Heaven and the earth will produce its fruit.