The end of the Torah portion describes the erection of the Mishkan:
And it was in the first month, in the second year, on the first of the month, that the Mishkan was erected. Moshe erected the Mishkan, and he fastened its sockets and set its boards and inserted its bars and erected its pillars. He spread the tent over the Mishkan and set the covering of the tent over it, as God commanded Moshe. (Shemos 40:17-19)
When we are told here that "Moshe erected the Mishkan," this refers to the lower curtains, for the Sages tell us:
Only the Mishkan itself is called Mishkan; the beams are not called Mishkan. (Shabbos 28a)
The word mishkan does not refer to the beams themselves, but to the first layer of material that covered the beams. This is confirmed by Rashi's commentary on the phrase "he spread the tent," which he claims refers to the goat-hair covering which was laid on top of the lower curtain. Thus, by this stage in the verse, those lower curtains were already in place. So the order of the erection of the Mishkan now becomes clear: first the lower curtains were spread, and only then were the beams put in place, after which the upper goat-hair covering was spread. The Seforno confirms this sequence of events:
Moshe erected the Mishkan - the ten skillfully woven curtains which are called Mishkan were erected before the beams. (Seforno, Shemos 40:18)
This is quite remarkable - the curtains were spread before the supports were placed underneath! This meant that this occurred:
...either by people holding up the curtains [while the beams were put underneath] or by miraculous means... (Ibid.)
What was the necessity for all this? Surely it would have been more practical to erect the beams and then spread the coverings over them. What possible purpose could this obscure order of construction fulfill?
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THE PURPOSE OF THE MISHKAN
The Mishkan was intended to be a location where the Divine Presence rested and was more palpable than in any other place in the world. The very name Mishkan means "dwelling place," and, indeed, in introducing the concept of the Mishkan, the Torah proclaims:
Make a sanctuary for Me, and I shall dwell within them. (Shemos 25:8)
This means that every aspect of the Mishkan contributed to this aim - the building itself and each vessel within it needed to be designed to receive and transmit the Divine Presence. This is not dissimilar to the relationship between the body and soul within each person. The body is a vehicle for the soul's existence in this world; so, too, were the details of the Mishkan the means by which God's Presence could be perceived on earth.
The right of klal Yisrael to benefit from this wonderful Mishkan was a great gift from God. For after the sin of the Golden Calf, they were in a spiritually bereft state and hardly suited to such a tremendous manifestation of the Divine. However, God granted them the Mishkan, enabling them to perceive Him even while they were in a spiritually inferior situation. At this stage they had been spiritually animated enough to realize that they were dissatisfied with the mere hope that God would rest among them. Instead, they knew that their task in life was to be, like the vessels in the Mishkan, vehicles for the Divine.
This was symbolized by the order of construction that we have mentioned. For the lower coverings were spread before the beams were put underneath to support them. This represents the people who, after the sin of the eigel, were given a Mishkan before they were really able to support the spiritual level it represented. Only after the curtains had been spread could the beams be put underneath. So, too, after the spiritual lift provided by the construction of the Mishkan the people could support the level they had been granted by God.
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A similar idea applies to the situation in which klal Yisrael found themselves in Egypt. It is well known that they had reached the lowest level of spiritual pollution in Egypt; just a short time longer in slavery may have meant that they would have been so immersed in Egyptian culture that they would have been irredeemable. As we know, God redeemed them then even though they were not really worthy of His attentions. But they were worth redeeming for what they could achieve: the acceptance of the Torah seven weeks later at Mount Sinai. So God took them above the level that they were on, granting them a great Exodus from Egypt, confident that they would "catch up," as it were, through their own efforts, in the seven intervening weeks.