Due to the inequities of the generation of the destruction of the Holy Temple, the forces of the Other Side [the kelipot]1 extended a membrane from all directions surrounding Eretz Yisrael towards the middle of the opening [above the Land, as mentioned above]--to the extent of sealing off the flow of divine connection from the supernal Jerusalem with the physical Jerusalem, hence the destruction.

We must bear in mind that when the membrane of the Other Side interfered, they didn't seal up the opening at one time [of the destruction], rather the consequences of the idolatry and other transgressions drew forth those forces little by little, until the opening was completely sealed, then came the destruction. We see from the first destruction an example of this. In that first destruction, the exile started with the portion of land under control of the ten tribes, gradually working its way to the kingdom of Judah and finally to the place of Zion, the temple, which is the center of the world.

The Land itself is inherently holy…

Now we must know that the Land itself is inherently holy, having been apportioned by G‑d as special, as opposed to the rest of earth. Being thus, how is possible for the kelipot to enter this G‑dly portion of land? Therefore the answer to this question is that in truth the kelipot have absolutely no portion in the Land. The best way to understand the phenomena is by parable: A landowner has a servant who has fled his master's servitude. Instead, he works for another man. One day the original master walks in, finds his servant, and takes him back to where he belongs. So too, the Jewish people have acquired for themselves a master through their transgressions. This "master" is the kelipot, and daily they sacrifice and serve their master. Yet they live in a land not belonging to their "master"; the kelipot have the right to enter the Land of Israel and take what is "rightfully" theirs, forcibly removing them [their "servants"] to their lands. Yet immediately after that, the gate is reopened. One may ask if the holiness returned to its original place, then how could the Land remain in a state of destruction? The answer is, that the Shechina ascended to its heavenly abode, while the Jews were exiled from their land to the land of the gentiles, leaving the land desolate without her children or husband. Therefore it wasn't significantly re-inhabited until that time when G‑d gazed down from the heavens. The holiness left in order not to dwell amongst the impurity, for that is its custom, as is known from the secret of tumat met [in Hebrew, impurity from the dead].2 That being the situation, G‑d has placed a curtain of holiness in that opening in that firmament above the Land of Israel, thus creating a partition between the impurity and the holiness. The Land is likened to an aguna 3 who can not marry another.

Israel remains desolate…from a lack of fulfilling positive mitzvot

The intention of this curtain [according to Rav Chaim Vital's transmission of the Arizal's teachings] is: It is known that at the time the malchut clothes itself with gevura and din [judgment]. At that time the din functions through the external-most garment, which is the hue of techelet4 which completes [from the root of the word "chole", which means to finish] everything. Thus at that point even the chitzonim [external forces] fear the malchut, as the wrath of the King. Therefore when the external forces see the malchut thus clothed, they flee from there. That is the essence of the "light covering" as is mentioned in the holy Zohar (part two page 141) which is the secret of the outermost garments, which in the end are the innermost garments; they are also called the 'holy curtain' relative to the internal garments. Therefore the external forces can't enter there. So too, the blessing and bounty are prevented from entering due to the might of the din that is incorporated in that veil. That din prevents the descent of the blessings which is all a result of the lack of merits and abundance of inequities amongst the Jews. That is why the land of Israel remains desolate: not because of the impurity, rather from a lack of fulfilling positive mitzvot.