Says the Rambam [Beis Habechirah 6-16]
Why do I say that the original consecration sanctified the Temple and Jerusalem for eternity, while in regard to the consecration of the remainder of Eretz Yisrael, in the context of the Sabbatical year, tithes, and other similar [agricultural] laws, [the original consecration] did not sanctify it for eternity?7
Because the sanctity of the Temple and Jerusalem stems from the Shechinah, and the Shechinah can never be nullified. Therefore, [Leviticus 26:31] states: "I will lay waste to your Sanctuaries." The Sages declared: "Even though they have been devastated, their sanctity remains."
In contrast, the [original] obligation to keep the laws of the Sabbatical year and tithes on the Land stemmed from the fact that it was conquered by the [Jewish people, as a] community. Therefore, when the land was taken from their hands [by the Babylonians,] their [original] conquest was nullified. Thus, according to Torah law, the land was freed from the obligations of the Sabbatical year and of tithes because it was no longer Eretz Yisrael.
When Ezra returned [to Eretz Yisrael] and consecrated it, it was not sanctified by means of through conquest, but rather through Chazzakah. Therefore, every place which was repossessed by the [exiles returning from] Babylon and consecrated when Ezra consecrated [the land] the second time, is sacred today.
Thus, as explained in Hilchot Terumah, it is necessary to keep the laws of the Sabbatical years and the tithes [on this land] even though it was taken from [the Jewish people in later years].
The Kessef Mishnah finds these statements contrasting to original conquest when we came from Egypt and the second time under the leadership of Ezra difficult to accept because of the following questions:
a) On what basis is Chazzakah considered a more effective means of acquisition than conquest?
b) After the initial conquest of Eretz Yisrael, the Jewish people manifested their ownership over it and thus, effected a Chazzakah. If so, why is Ezra's Chazzakah, which was not preceded by conquest, more effective than the Chazzakah which followed the original conquest? Why should the conquest detract from the consecration of the land?
These questions can be answered as follows: The Talmud Yerushalmi (Challah 5:1) interprets Genesis 15:18: "I have given this land to your seed to mean that from Abraham's time onward Eretz Yisrael became the property of the Jewish people. Though the land was still possessed by the Canaanites, the Jews were already its legal owners. [See Bava Batra 119b].
Despite this claim of ownership, the sanctity of Eretz Yisrael came about only after the Jewish people entered the land, after the redemption from Egypt. At that time, they were commanded to conquer the land and take it forcefully from the Gentiles (See Numbers 32:29, Deuteronomy 3:21, etc.) Since God made the consecration of the land dependent on its conquest by Israel, it follows that conquest by a Gentile nation can nullify that holiness.
In contrast, Ezra was not commanded to reconquer Eretz Yisrael, but to settle it. In this instance, God made the sanctity of the land dependent on the Jewish people manifesting their ownership over the land which had been given to them as an eternal inheritance. Since Eretz Yisrael remains our land, regardless of how many times it has been conquered by Gentiles, the sanctity effected by that manifestation of ownership is also eternal. See Likkutei Sichos, Vol. 15, 102-109.
ולמה אני אומר במקדש וירושלים קדושה ראשונה קדשה לעתיד לבוא ובקדושת שאר א"י לענין שביעית ומעשרות וכיוצא בהן לא קדשה לעתיד לבוא לפי שקדושת המקדש וירושלים מפני השכינה ושכינה אינה בטלה והרי הוא אומר והשמותי את מקדשיכם ואמרו חכמים אע"פ ששמומין בקדושתן הן עומדים אבל חיוב הארץ בשביעית ובמעשרות אינו אלא מפני שהוא כבוש רבים וכיון שנלקחה הארץ מידיהם בטל הכבוש ונפטרה מן התורה ממעשרות ומשביעית שהרי אינה מן ארץ ישראל וכיון שעלה עזרא וקדשה לא קדשה בכיבוש אלא בחזקה שהחזיקו בה ולפיכך כל מקום שהחזיקו בה עולי בבל ונתקדש בקדושת עזרא השנייה הוא מקודש היום ואף על פי שנלקח הארץ ממנו וחייב בשביעית ובמעשרות על הדרך שביארנו בהלכות תרומה:
Why do I say that the original consecration sanctified the Temple and Jerusalem for eternity, while in regard to the consecration of the remainder of Eretz Yisrael, in the context of the Sabbatical year, tithes, and other similar [agricultural] laws, [the original consecration] did not sanctify it for eternity?7
Because the sanctity of the Temple and Jerusalem stems from the Shechinah, and the Shechinah can never be nullified. Therefore, [Leviticus 26:31] states: "I will lay waste to your Sanctuaries." The Sages declared: "Even though they have been devastated, their sanctity remains."
In contrast, the [original] obligation to keep the laws of the Sabbatical year and tithes on the Land stemmed from the fact that it was conquered by the [Jewish people, as a] community. Therefore, when the land was taken from their hands [by the Babylonians,] their [original] conquest was nullified. Thus, according to Torah law, the land was freed from the obligations of the Sabbatical year and of tithes because it was no longer Eretz Yisrael.
When Ezra returned [to Eretz Yisrael] and consecrated it, it was not sanctified by means of through conquest, but rather through Chazzakah. Therefore, every place which was repossessed by the [exiles returning from] Babylon and consecrated when Ezra consecrated [the land] the second time, is sacred today.
Thus, as explained in Hilchot Terumah, it is necessary to keep the laws of the Sabbatical years and the tithes [on this land] even though it was taken from [the Jewish people in later years].
The Kessef Mishnah finds these statements contrasting to original conquest when we came from Egypt and the second time under the leadership of Ezra difficult to accept because of the following questions:
a) On what basis is Chazzakah considered a more effective means of acquisition than conquest?
b) After the initial conquest of Eretz Yisrael, the Jewish people manifested their ownership over it and thus, effected a Chazzakah. If so, why is Ezra's Chazzakah, which was not preceded by conquest, more effective than the Chazzakah which followed the original conquest? Why should the conquest detract from the consecration of the land?
These questions can be answered as follows: The Talmud Yerushalmi (Challah 5:1) interprets Genesis 15:18: "I have given this land to your seed to mean that from Abraham's time onward Eretz Yisrael became the property of the Jewish people. Though the land was still possessed by the Canaanites, the Jews were already its legal owners. [See Bava Batra 119b].
Despite this claim of ownership, the sanctity of Eretz Yisrael came about only after the Jewish people entered the land, after the redemption from Egypt. At that time, they were commanded to conquer the land and take it forcefully from the Gentiles (See Numbers 32:29, Deuteronomy 3:21, etc.) Since God made the consecration of the land dependent on its conquest by Israel, it follows that conquest by a Gentile nation can nullify that holiness.
In contrast, Ezra was not commanded to reconquer Eretz Yisrael, but to settle it. In this instance, God made the sanctity of the land dependent on the Jewish people manifesting their ownership over the land which had been given to them as an eternal inheritance. Since Eretz Yisrael remains our land, regardless of how many times it has been conquered by Gentiles, the sanctity effected by that manifestation of ownership is also eternal. See Likkutei Sichos, Vol. 15, 102-109.
It has also been noted that after the קנין of כיבוש, the קנין of חזקה is meaningless. You can't acquire what already belongs to you. So the all they really had the first time was כיבוש as opposed to the second time when they had חזקה. So כיבוש [of another nation] can nullify כיבוש whereas the חזקה we made the second time around was forever.
