In our Parashah, the Torah defines the place where the Holy Temple will be erected with the pseudonym "the place that God will choose." This teaches that the sanctity of the Holy Beit Hamikdash rests not only on the building and its furnishings and equipment, but on the place itself—the Temple Mount—the place that God chose.
This also explains the difference between the Mishkan, the portable Sanctuary, and the Beit Hamikdash, the Temple. The Mishkan was entirely on a flat surface, with no differences in height between its sections. In contrast, regarding the Temple, Rambam says: "The Temple was not entirely on a flat surface, but rather on the slope of a mountain." He then goes on to describe the steps a person ascended when moving from one level of holiness to a higher one. Why don't we find the same in the Mishkan (the portable Sanctuary)?
THE PLACE HAS ACQUIRED HOLINESS
The essential difference between the Mishkan and the Beit Hamikdash was that the Mishkan was a temporary structure, as it is written: "And I will transmit in a tent and in the Mishkan," while the Beit Hamikdash, the Temple, was a permanent structure. In the words of Rambam: "Once the Temple in Jerusalem was built, all sites were forbidden for erecting a house for Hashem and offering sacrifices there, and there was no concept of ceasing, for all generations except in Jerusalem and on Mount Moriah.”.
This reveals a fundamental difference in the type of sanctity they possessed: in the Mishkan, a temporary structure, sanctity resided primarily in the building itself and its components—the partitions, the curtains, and so on. The site on which the Mishkan stood was not sanctified, and after the Mishkan was moved to another location, its sanctity did not remain. In contrast, in the Beit Hamikdash, sanctity resided in the site itself, to the point that even after the Temple's destruction, the site retained its sanctity, for it was "the place that God will choose.".
HEIGHT DIFFERENCE
Since holiness was expressed only within the Temple itself in the Beit Hamikdash, this was reflected in the varying heights of its different parts, with the most sacred being the highest. In contrast, in the portable sanctuary, where holiness did not permeate the physical space, this was not reflected in the elevation of the ground, and the entire Mishkan was built on flat land.
We learn from this that the emphasis placed on the different heights of the various parts of the Temple in Jerusalem—as legislated by Rambam—is precisely what reflects the uniqueness of the Temple over the mobile Sanctuary, since the latter constitutes "the place that Hashem will choose," and therefore the level of holiness is reflected in the very height of the land.
EXCEEDS ALL RATINGS
What remains to be understood is why the two most sacred levels of the Temple, the Kodesh—the "holy" area, where the menorah, incense, etc., were located—and the Kodesh HaKodashim—"the Holy of Holies," where the Ark of the Covenant was kept—were both on the same level? Did the latter far surpass it in holiness?
The explanation for this is that the different levels of height reflected measurable levels of holiness, expressed in terms of greater or lesser height. Therefore, one could speak of the degree to which one level surpassed another by expressing it in terms of building height. But in the Kodesh haKodashim, the "holy of holies" environment contained a holiness so profound that it could not be classified or defined proportionally or on any other level. There dwelt the very Essence of God. His holiness cannot be expressed (not even allegorically) through the height of a physical place, which by its very nature and definition is limited and quantifiable.
(Likutei Sichot volume 29 Page 71)