This week's Parsha begins with a continuation of the list of responsibilities of the Leviyim, namely, the families of Gershon, Kehos, and Merari. In general, it was their job to take apart and carry the Mishkan every time the Jews traveled through the desert, until they were able to set up camp at a different location where they would then reassemble it. One of the notions that is found when examining the different jobs of the Leviyim is that when they were to carry the various Keilim, the vessels, of the Mishkan, particularly those which are positioned in close proximity to the Kodesh HaKodashim, the place in which the Shechinah was "contained," so to speak, those items had to be covered and not seen. The Torah warns "ולא יבאו לראות כבלע את הקדש ומתו," meaning, in effect, that if one sees the "holy things" when they are not covered, one will die (במדבר ד':כ').
How can we understand this? Why are we not allowed to look at these vessels; what is so special about them? Why, as alluded to in our Parsha (שם פסוקים כ"ה-כ"ו), were there always so many coverings on top of the Mishkan? Perhaps we may understand this by comparing the Mishkan, and what it represented, to Ma'amad Har Sinai, when Hashem appeared to Bnai Yisrael. The significance of Har Sinai is identified by Hashem's presence there on that special occasion; the significance of the Mishkan is similarly identified by Hashem's continued presence there. It is interesting to note that when the Pesukim describe Hashem involved in "גילוי שכינה," revealing Himself at Har Sinai, they relate that Hashem does so only in a somewhat hidden form, in the presence of smoke and fire, as the Posuk states, "והר סני עשן כלו מפני אשר ירד עליו ה' באש," "and Har Sinai was filled with smoke, because Hashem had come down on it in the form of a fire" (שמות י"ט:י"ח). Perhaps because at Har Sinai, when Hashem revealed Himself, it was only under the facade of a lot of smoke, the only reason that Bnai Yisrael were allowed to look upon the Shechinah was because it was in fact covered and hidden by the smoke. But if the Shechinah would have been revealed in its purest fashion, the people would undoubtedly not have been able to gaze upon it and live, as even Moshe himself was told later on, "לא יראני האדם וחי," "no person can see Me and live" (שם ל"ג:כ'). This is why Hashem had to cover His Shechinah in smoke. But in the Mishkan, there was no smoke. The Shechinah resided in the Kodesh HaKodashim on or near the various vessels, and was totally revealed, without obstruction. Consequently, it was forbidden for any mortal man to gaze at this, and even those vessels which had the presence of the Shechinah directly on or even near them, therefore had to be covered and hidden from view.
This idea may also perhaps explain the interesting practice of the Kohein Gadol during his yearly visit to the Kodesh HaKodashim on Yom Kippur. In the midst of the day's Avodah, the Kohein Gadol walks backwards into this holiest of all rooms, takes the Ketores, the incense, and burns it on the Mizbeiach, and leaves, and only a little later comes back to do the rest of the Avodah. Why does he first go in backwards and burn the Ketores? Some suggest that it is because the Ketores, the incense, when burnt, creates a lot of smoke. Even the Kohein Gadol, due to the intense concentration of the Shechinah in the Kodesh HaKodashim, is not allowed to look upon the pure, unobstructed Shechinah. The Kohein Gadol must therefore first go in backwards (so as not to see anything), and burn the Ketores (which creates a lot of smoke), so that when he comes back later, the room will be full of smoke, and he may then look upon the Shechinah and do the rest of the Avodah, for the Shechinah then is hidden in smoke, just as it was on Har Sinai.
Based on this idea, it may be possible to suggest that the Mishkan was actually greater than Har Sinai, for the Mishkan contained the pure, unadulterated Shechinah, while at Har Sinai, the Shechinah was covered with smoke. Perhaps, then, Har Sinai might have been intended only as the source of our relationship with Hashem, as we signed a Bris (covenant) with Him there (עיין שמות כ"ד:ד'-ח'), but Har Sinai in no way represented the apex or the pinnacle of our relationship with Hashem, for the Mishkan had a higher status. In the Mishkan, Hashem's relationship with Bnai Yisrael (by means of the Shechinah which dwelled therein) was not only maintained, but was greatly amplified and expanded, as seen by the fact that the presence of the Shechinah there was pure and unadulterated, and did not need to be covered by smoke. Only from the outside did the Shechinah have to be covered with the various coverings that rested on the Mishkan, and only when moving did the special vessels have to be covered. But on the inside, when the Mishkan was in operation, the Shechinah was there and visible.