Or HaChaim on Leviticus 25:29/אור החיים על ויקרא כ״ה:כ״ט

1 ואיש כי ימכר בית מושב, "And if a man sells a house which is (his) residence, etc." After the Torah has described how G'd "sold" the Temple, the Torah now explains how it could happen that G'd would "sell" His heritage, the Holy Temple. This is why the paragraph starts with the word ואיש, so that we understand that the word refers to G'd, just as it had in the previous paragraph. The extraneous word מושב refers to the house in which G'd has His residence, the Holy Temple; the expression עיר חומה refers to Jerusalem, the "walled city" which is described by David in Psalms 125 ,2 as "the city ringed by mountains, (i.e. like wall)." The Torah continues by explaining that these very "walls" are why the city may be be redeemed after as little as a year already. The reason is similar to what has been revealed to us by Midrash Tehillim on Psalms 79,1. We were told there that when G'd vented His anger on the stones and timber of the city allowing it to be destroyed, this was in lieu of venting all His anger on the people inside the city. Had G'd not vented His anger on stone and wood, not a single Jew would have survived that experience. If Israel had been wiped out, there would never again have been either a Holy Temple or a city of Jerusalem.