Bearing in mind that the Cana'anim were not yet expelled from their land, why does the Torah write (in the previous Pasuk) "Vataki ha'Aretz es Yoshvehah" (in the past)?
Ramban #1: Because once the decree to expel them had been issued, it was as if it had already been implemented. 1
Ramban #2: The Pasuk means that Hashem has already expelled them above (with reference to their angel). 2
See Oznayim la'Torah, who elaborates.
As the Pasuk indicates in Bamidbar 14:9 (Ramban, according to his explanation of the Pasuk).
Why does the Torah insert the word "Atem"?
Sifra: To teach us that Yisrael are worthy of the Parshah of Arayos, since they already kept it in Egypt. 1
Oznayim la'Torah: To emphasize that, although the Cana'anim were guilty of all the abominations listed in the Parshah, Yisrael should avoid trenasgressing even one of them.
As the Midrashim explain, commenting on the Pasuk in Shir ha'Shirim, 4:14 "Gan Na'ul Achosi Kalah" ([See Malbim]). See also Or ha'Chayim on this Pasuk.
What are the Chukim and Mishpatim to which the Pasuk is referring?
Seforno: They refer to keeping away from adultery and punishing those who don't, respectively.
Why does the Pasuk add "ve'Lo Sa'asu mi'Kol ha'To'evos ha'Eileh"?
Seforno: What the Torah is saying is that "If You will avoid contravening the minor Isurim you will not transgress the major ones. 1
Refer to 18:30:1:1*. Because it is due to the fact that the nations were guilty of K'reivah and Giluy Arayos (literally), that they went on to perform adultery and incest, which resulted in their subsequently expulsion from Eretz Yisrael (Seforno).
