How will we reconcile this Pasuk, which states that Yisrael should not ascribe their inheriting Eretz Yisrael to their own righteousness and to the evil of the seven nations, with Pasuk 5, which ascribes it to the evil of the seven nations?
Rashi: The Pasuk means that one should not ascribe it both to Yisrael's righteousness and the evil of the nations, 1 but to the evil of the nations exclusively.
Ramban and Rashbam: The Pasuk is saying that they should not ascribe the destruction of the Cana'anim to their evil and their inheriting Eretz Yisrael to their own righteousness, 2 because whereas the first assumption is correct, 3 the second one is not - as the Pasuk goes on to explain.
Seforno: The Pasuk is saying that, upon seeing the miraculous way in which they will defeat the Cana'anim and they realize that Hashem is fighting on their behalf, they should not ascribe their victory to their righteousness, in order that they come and inherit the land quickly, because it is due to their evil that would Hashem drive them out before us. 4
In other words, the 'Vav' in "u'v'Rish'as" means 'and', not 'or'.
Rashbam: Due to their superiority over other nations.
Ramban: Which explains why He was about to destroy them, as the Pasuk goes on to explain.
This is how the Seforno explains "uv'Rish'as ha'Goyim ha'Eileh ... " in this Pasuk - interpreting the 'Vav' as if it had written "Ki".
What is the connection between the current Pesukim and the previous Parshah?
Ramban: The Torah is coming to negate the notion 1 that, having ascertained that Yisrael defeated the Cana'anim due to Hashem's participation, He granted them victory based on their righteousness; and in fact, they only inherited it due to Hashem's promise to Avraham. 2
How will we reconcile the current Pesukim, which describe Yisrael as unworthy and stubborn, with the Pasuk above (7:8), which talks about Hashem's love of Yisrael?
Ramban: The current Pasuk is referring to this particular generation, which rebelled against Hashem from the moment they entered the desert, whereas the Pasuk above is referring to Yisrael in general.