Why does the Torah repeat the word "Vehorashtem es ha'Aretz"?
Rashi: Because it is not a Mitzvah but a promise - that if they expel the inhabitants of the land, they will be able to settle it and remain there, otherwise not!
Ramban: This Pasuk is presenting a Mitzvah to dwell in Eretz Yisrael and possess it, and if one decides to go and conquer Bavel, Ashur or any other country and to live there, one will contravene an Asei. 1
Seforno: This is a promise that if they destroy the inhabitants of the land, they will be able to pass it on to their heirs as an inheritance, otherwise not! 2
Ramban: When the Gemara in Kesuvos 110b, stresses the obligation to reside in Eretz Yisrael, placing a prohibition against leaving it and labels a woman or a man who refuses to move there with his or her spouse 'a Moredes' (a rebel), it does so based on this Pasuk.
Seforno: Even if they themselves succeed in conquering it.
