Or HaChaim on Genesis 47:23/אור החיים על בראשית מ״ז:כ״ג

1 הן קניתי אתבם היום. "Look, I have bought you today, etc." The reason Joseph added the word היום, and the fact that it does not appear after the report that Joseph had bought their land, is to tell us that the method of acquisition was that each individual was acquired by the method known in Jewish law as משיכה, i.e. drawing the object being purchased a short distance towards the purchaser, as customary when one purchases slaves (Kidushin 22). Joseph did this en masse by transferring whole populations from city to city. Since one cannot acquire land by moving it, the word היום was interposed between these different kinds of purchases Joseph made.

2The Torah also wanted to clarify something else here. We have the principle (Pessachim 88) that when one acquires a slave one automatically acquires everything this slave owned at the same time. There was no need to mention the acquisition of these Egyptians' lands separately. Since it is possible that Joseph did not acquire these Egyptians in the manner one usually acquires slaves, but that they became his (Pharaoh's) slaves only to the extent that they had to continue to farm the lands they had farmed previously and pay a portion of their harvest to Pharaoh, the Torah distinguished between the acquisition of the people on the one hand and that of their lands on the other hand. In practice, these Egyptians became hired hands who were not free to leave their employment. As a result Joseph had to acquire the land separately. This is why the Torah wrote in verse 20 that "Joseph acquired all the lands on behalf of Pharaoh as each of the Egyptians sold his land, etc." This would enable Pharaoh to bring in other labourers to work these fields, whereas he was not able to force the Egyptians who had previously owned those fields to farm them as he did not own those farmers bodily. When Joseph said: "I have acquired you," he meant that he had acquired them as hired hands, as distinct from their lands which he had acquired outright.