Megillah 10B

השתא [הא] אמרי לא צריכא לקדושי! אלא: מצאו את אלו ומנאום.

Now, didn’t they say later in the same baraita that it is not necessary to consecrate them? Rather, this is what the baraita means to say: It is due to the fact that when the exiles ascended from Babylonia they discovered these and enumerated them.

ולא אלו בלבד, אלא כל שתעלה לך מסורת בידך מאבותיך שמוקפת חומה מימות יהושע בן נון ⁠— כל המצות הללו נוהגין בה, מפני שקדושה ראשונה קידשה לשעתה וקידשה לעתיד לבא. קשיא דרבי ישמעאל אדרבי ישמעאל.

The baraita continues. And not only these, but in any city with regard to which you receive a tradition from your ancestors that it was surrounded by a wall from the days of Joshua, son of Nun, all these mitzvot are observed in it, due to the fact that the initial consecration sanctified Eretz Yisrael for its time and sanctified Eretz Yisrael forever. This is difficult, as there is a contradiction between one statement of R' Yishmael and another statement of R' Yishmael.

תרי תנאי אליבא דרבי ישמעאל ברבי יוסי. ואיבעית אימא, הא רבי אלעזר בר יוסי אמרה, דתניא: רבי אלעזר ברבי יוסי אמר: ״אשר לוא חומה״, אף על פי שאין לו עכשיו והיה לו קודם לכן.

The Talmud answers: This is a dispute between two later tanna’im, who hold according to the opinion of R' Yishmael, son of R' Yosei. Each transmitted R' Yishmael’s opinion in a different manner. And if you wish, say instead that one of the traditions is mistaken, as with regard to this statement, R' Elazar bar Yosei said it, as it is taught in a baraita: R' Elazar, son of R' Yosei, said that the verse states: “Which has [lo] a wall” (Leviticus 25:30). The word lo is written with an alef, meaning no, that it does not have a wall, but its vocalization is in the sense of its homonym, lo with a vav, meaning that it has a wall. This indicates that even though it does not presently have a wall, as it was destroyed, but it had a wall previously, it retains its status as a walled city. It is R' Elazar, son of R' Yosei, who maintains that the first consecration sanctified Jerusalem forever.