Why is it called 'Me'aras ha'Machpeilah'?
Rashi #1: Because it consisted of two stories, a ground floor and an attic (or two rooms, one within the other 1 ).
Rashi #2: Because only couples were buried there. 2
Ramban #1: That was the name of the cave. 3
Ramban (citing Midrash): Because Hashem 'folded Adam's height' (who was 100 Amos tall) before burying him there.
Seforno and Rashbam: The entire area (valley) was called 'Machpeilah'.
Why did Avraham say "v'Yiten", an expression of a gift, and also "for the full price"?
Ramban #1: Because he considered it a gift for which he was willing to pay - in full. 1
Ramban #2: It is a manner of speech to say Yiten [even] for sales.
Ohr ha'Chayim: Avraham was wise to use an expression of a gift, lest Efron contest the sale in the future, saying that he did not know its value, especially according to the Zohar, that the cave was always dark and he never saw inside.
Malbim: It will be a gift, lest it violate the custom (refer to 21:8:1:3*). Also the money I will give is also a gift, and not like a sale.
Seforno: Avraham was concerned that Efron does not want to sell for a discount, but he may feel pressured to do so, to honor you (who ask him on my behalf). (Alternatively - it is an honor for the Mitzvah to pay in full and not to haggle over the price - like David when he purchased the location of the Beis-Hamikdash from Aravnah ha'Yevusi (See Divrei-ha'Yamim 1, 21:24).
Seeing as there was only one cave that fitted the description 'Me'aras ha'Machpeilah', why did Avraham find it necessary to add "asher bi'Ketzei Sadeihu", and why did he add "la'Achuzas Kaver"?
Oznayim la'Torah: Avraham specified three reasons as to why Efron should agree to the sale: (a) He only asked for the cave and not for the field 1 in which it was situated; (b) He pointed out that the cave was at the edge of the field
Why did Avraham want specifically Me'aras ha'Machpeilah?