Why does the Torah see fit to repeat a detailed description of the location of the Me'aras ha'Machpelah?
Ramban #1: It is coming to tell us that the land of Chiti (which the Pasuk has mentioned until now) is situated in Eretz Kena'an 1 (alias Eretz) Yisrael - to teach us that Sarah was buried in Eretz Yisrael.
Ramban #2: To teach us that, although Avraham lived a long time in Eretz P'lishtim, from where he moved to Chevron and back to P'lishtim again, Chevron is part of Eretz Kena'an and not Eretz P'lishtim. And that there is where Sarah Imeinu is buried.
Refer to 23:19:153:2.
It is not however, clear why this is necessary, since we already learned above (10:15) that Ches was the son of Kena'an. (EC)
Why does the Torah find it necessary to record the full story of Sarah's burial?
Ramban #1: To teach us that the Berachah said to Avraham (12:2) "And I will make your name great and you will be a B'rachah!" came true in his lifetime - How he became 'a prince of G-d' in the country where he came to sojourn, how they all called him 'Adoni' and the respect that they showed him. Moreover we see how Sarah was respectfully buried in Eretz Yisrael.
Ramban #2: It is important to know where the Avos ha'Kedoshim are buried, so that one can honor the place. 1
Ramban (from Bava Basra 16a): This was one of Avraham Avinu's ten tests, that when it came to burying Sarah, he had to purchase a burial-ground on her behalf [even though Hashem promised the land to him, and he was not upset with Hashem].
Malbim (Torah Ohr): Avraham planted in Bnei Ches Emunah that the soul remains after death; the soul will return in its garment (the body), therefore it is important to bury one amidst his family, and a Tzadik among Tzadikim. He paid a fortune, and taught this to them. The Midrash (refer to 23:20:151:1) compares this to Aseres ha'Dibros, which also clarify Emunah, reward and punishment.
And pray there., like we find that Kalev did
It is clear from the verses that Avraham buried her afterwards. Why must the Torah say "v'Acharei Chen"?
Ohr ha'Chayim: A Nochri who sells a field, when he gets the money, it becomes Hefker. The Yisrael acquires only when he gets a document [or makes a Chazakah].
Ha'Emek Davar: This teaches that Avraham acquired it before burying her, for it is disgraceful for a Tzadik to be buried in a grave that is not his (Bava Basra 112a).
Why does it say "Sedei ha'Machpelah"?
Malbim: The field became secondary to the cave. It was not for planting, rather, a field in front of the cemetery.
Ha'Emek Davar (49:30): The word Machpelah is used for the cave, the valley, and the field (verses 9, 17, 19). In their lifetimes, the Avos were 'extended' like an open Sefer Torah; we learn from every action and word of theirs. After death, they are folded up and hidden, like a closed Sefer. Avraham, the first of the Avos, "ha'Adam ha'Gadol ba'Anakim" (Yehoshua 14:15), amidst his great Kedushah, was constricted to the cave itself.
It already says (13:18) that Elonei Mamrei is in Chevron. Why is this repeated here?
Malbim: Initially it was called Kiryas Arba due to 'Arba', the father of the giants, or the four giants there. 1 Avraham changed the name to Chevron, for there Yischabru (will be connected) couples who were pleasant [to each other] in their lifetime, and will not be separated in death. 2
Ha'Emek Davar: Just like there is a special Segulah of burial in Me'aras ha'Machpelah (only awesome people were buried there), there is a Segulah of burial in Chevron (but it is not as great). It adds "b'Eretz Kena'an" to teach that there is a Segulah of burial in Eretz Kena'an.
Why does it say "El Me'aras", and not b'Me'aras?
Ha'Emek Davar (49:29): "El" implies completing the purpose. The cave was created for the Avos and Imahos to be buried there. It says "El" when the first was buried there, and also regarding the last (Yakov