Or HaChaim on Genesis 23:19/אור החיים על בראשית כ״ג:י״ט

1ואחרי כן…ויקם השדה. Afterwards the field stood as burial plot, etc. We need to understand why the Torah had to write the words: "afterwards," something that is obvious. What could be more natural than Abraham burying Sarah at the end of these negotiations? Besides, why did the Torah repeat the words: ויקם השדה, something we read already in verse 17?

2The Torah wanted to confirm that the transaction complied with all and every legal form of acquisition. The words "afterwards" mean that once Abraham had weighed the money for Efron the latter had foregone all claim to that property in perpetuity. Maimonides explains it thus in chapter one of Hilchot Zechiyah Umatanah: "A Gentile loses his right to formerly owned property the moment he accepts the money as compensation for it. A Jew, on the other hand, does not acquire title to his new property until he has a written document. Once this has occurred the property in question is like land in the desert which anyone can stake a claim to." In other words, once the Gentile has accepted the money he loses all former claims. Had Abraham buried Sarah before giving the money to Efron, the fact that he gave the money to Efron afterwards would not have made a full acquisition, seeing that the act of possession expressed by his burying Sarah would not have been performed on land owned by him at the time.

3We need to examine if the act of חזקה, i.e. using the land for one's own purpose, is actually legally valid when the act of such חזקה is performed on land previously owned by a Gentile. In chapter two of the above-mentioned tractate of Maimonides, he writes as follows: "In the case of formerly ownerless property, or property formerly owned by a proselyte, the fact that the squatter (Jewish) has eaten the proceeds of such land for a number of years does not constitute an act of acquisition of either tree or the land itself until such time as the squatter has performed an act on the body of the land itself. What kind of activity would qualify in such an event? In the case of a Jew having taken over the house of a proselyte or an abandoned house, if he whitewashed it or added a moulding about 60 centimeters high this would constitute a valid act of acquisition. If he took earth from high ground and transferred it to fill lower ground in the same piece of land this would be considered as an improvement of the earth and would qualify as an act of acquisition." It is clear therefore that if the squatter merely shifted some earth without specific intent to effect an improvement on that soil- even though he thereby levelled the ground,- this would not be enough to qualify under the heading of קנין, acquisition. Maggid Mishneh (a commentator on Maimonides) writes that if the squatter spread mats on the ground in order to be able to sit on it in comfort and to enjoy this, this would count as a valid act of קנין, acquisition. An alternative cited by the above commentator suggests that even spreading the mats merely in order to improve the appearance of the ground in question suffices. Rabbi lbn Migosh concurs with the latter example. Thus far the quotation from Hilchot Zechiyah Umatanah. Granted that according to the first example cited by the Maggid Mishneh anyone who benefits from an act performed on the land he squats on performs a valid act of חזקה, Abraham benefited by having buried Sarah on that land and thereby performed an act of acquisition; however, according to the opinion of Rabbi lbn Migosh that an actual improvement of the land has to take place, Sarah's burial would not have constituted such an improvement. How then did Abraham acquire that land (even though Efron had forfeited it)?

4Perhaps the superstructure erected around the grave, and especially the sepulchral chambers dug within the earth which was customary at the time, constituted such an improvement in the field under discussion. These sepulchral chambers were probably white-washed with lime to prevent the earth around them from crumbling. Now we can understand the reason the Torah repeated the words ויקם השדה. It means that after Abraham had buried Sarah the acquisition of that field by Abraham became complete.