Sforno on Genesis 23:9/ספורנו על בראשית כ״ג:ט׳

1מערת המכפלה, a place known as machpela.

2Compare verse 17 ויקם שדה עפרון אשר במכפלה אשר בקצה שדהו, “Efron’s field which is situated in machpela at the edge of his field, stood, etc.” The details provided by the Torah are intended to prove to us, the reader, that by selling the cave to Avraham Efron did not suffer any loss of face, he had no reason to feel embarrassed about what he had done.

3בכסף מלא, I do not want that he grant me a reduction from its real worth as a gesture to you.

4בתוככם, in the presence of all of you. I do not ask for time to come up with the payment but am willing to pay cash at once. Compare verse 16 where Avraham does in fact pay cash immediately.

5לאחוזת קבר, Avraham wanted complete freedom to do what he wanted to in the property once he had acquired it. This is the privilege granted to anyone owning an ancestral heritage. Avraham wanted it understood that as a result of the sale Efron would not be able to dictate to him how close to his own property Sarah or other members of his family could be buried.