The Mishkan was a physical symbol of the continuation of the Divine revelation which began at Mt. Sinai, and it served as a home for the Tablets of the Covenant which were given at Sinai.1
Need for a home – On its simplest level, the Tabernacle was designed to house the Ark, which functioned as a safe deposit box for the Tablets. For Ramban, though, this connection also mystically transformed the Mishkan and the Ark into an extension of Mt. Sinai, thereby facilitating the continued Divine presence.3 In contrast, Cassuto explains that although Hashem can dwell amidst the people without the existence of any physical structure, it was the nation which needed to see a tangible building to reassure them of God's ongoing presence.4
Why now? – The command to build the Mishkan logically comes at this point, since it is an outgrowth of the revelation at Mt. Sinai and must house the Tablets which came from Sinai.
Chronology – According to this approach, the command to build the Mishkan is recorded in chronological order, as it flowed from the Sinaitic revelation and preceded (and was unconnected to) the sin of the Golden Calf.5
Ancient Near Eastern parallels – In the Ancient Near East, copies of treaties were often stored in the temples of the gods of the two parties,6 presumably both for their safekeeping and to instill fear of retribution for any transgressions from the divine witness. As the Tablets of the Law served as testimony to the covenant (or treaty) between the nation and Hashem, it is not surprising that they were similarly stored in Hashem's "Temple", the Mishkan.7
Biblical parallels – Ramban points to a number of linguistic and conceptual parallels which link the giving of the Decalogue at Mt. Sinai and the construction of the Mishkan.8 These highlight how the Tabernacle transformed the initial one-time revelation into a continuous one.9
Focal point – The Ark ("אֲרוֹן הָעֵדֻת") and the Tablets ("לֻחֹת הָעֵדֻת") are the raison d'être for the entire Mishkan, as it is there that God descended to commune with Moshe. Thus, the Tabernacle is referred to as "מִשְׁכַּן הָעֵדֻת". Ramban asserts that for this reason, the aron is also the first vessel commanded to be made.10
"וְשָׁכַנְתִּי בְּתוֹכָם" – This position maintains that these words provide God's explanation of the purpose of the building.
Altars for atonement – Ramban explains that by atoning for the nation's sins, the sacrifices insured that the Divine presence would not desert the sanctuary. Thus, the altars were subservient to the Ark which was the main focus of the Tabernacle.11
Tabernacle unmentioned before Moshe's ascent – According to this approach, God might have initially mentioned only the Tablets to Moshe, since they are what created the need for the Tabernacle.
Honoring Hashem
The Mishkan provided an opportunity for the people to give to and show respect for Hashem. It is the equivalent of the commandment to give of one's first fruits; in this case man's first creative work is consecrated back to God.
Need for a house – According to this approach, it is the process of building and dedicating a house to Hashem, rather than the resulting completed product, which is important.
Midrash Aggadah asserts that the nation desired to build a special place for God, as a way of glorifying Him. Turning to human models of relationship, the people thought to honor God in the way that subjects glorify a king, by building him a palace with a candelabrum, table, and incense.12
According to the Biur, consecrating a House for God was for the people's own benefit. In dedicating the first fruits of their building, the nation learned to recognize Hashem's hand in all they did and made.
Why now? – As the nation was about to enter the land and begin building an infrastructure, homes, and other institutions, it was incumbent on them to first consecrate their first building to Hashem.13
Chronology – The command to build the Tabernacle is in chronological order.
Parallels – The Biur compares this commandment to that of bikkurim, the giving of first fruits. Just as one must give the first of one's womb, land, and animals, so too one must consecrate the first of one's creative actions to Hashem.
Focal point – This position does not focus on any particular vessel or section of the Mishkan, but rather on the edifice as a whole.
"וְשָׁכַנְתִּי בְּתוֹכָם" – This approach would view this verse not as the ultimate purpose of the building but one of the practical benefits of the nation's gift to God.
Altars for atonement – These commentators do not explain the relationship between the building being a gift to God and its use as a site for sacrificial offerings and a means of atonement for sins.
No mention before ascent –
National Center
The Mishkan ensured the unity of the nation, providing a centralized location for all to gather in their worship of God.
Need for a house – Shadal suggests that the house served as a unifying communal center for the nation, helping to keep tribal divisions at bay and instill feelings of brotherhood as they gathered together in service of Hashem.14. In addition, the tangible building impressed upon the masses a full appreciation of the fact that God, their king, was in their midst.15 As such, the tabernacle was built in the likeness of a king's palace with all its trappings.16
Why now? Shadal asserts that God did not want to wait until the nation would finish the conquest so as to build this center, and thus commanded to build a portable house which could be set up anywhere.
Chronology – The story is in its chronological place.17
Focal point – This approach might suggest that the sacrificial service on the altar is the main focus of the Tabernacle, for that is what brought people to gather together.
"וְשָׁכַנְתִּי בְּתוֹכָם" – The fact that God chose to dwell in the Mishkan is what leads people to sacrifice and gather there.
Altars for atonement – Though Shadal does not emphasize the role of atonement, he does believe that the institution of bringing sacrifices for atonement to one centralized location helped unify the nation.
No mention before ascent – Shadal does not address this point.
A Corrective Measure
Atonement for Sin of Golden Calf
The Tabernacle was built to atone for the sin of the Golden Calf specifically. Through the use of gold in constructing a house for God, the people effectively undid the original making of the Golden Calf, allowing God to dwell amongst them once again.
Need for a house – Though God dwelled amongst the people before the sin even without a house, afterwards, the only way He was willing to return to their midst was if they built a Tabernacle for Him. The act of construction itself, more than the resulting building, was crucial for the nation to reconnect to God.
Chronology –
Achronological – Sifre and Tanchuma maintain that the command to build the Tabernacle is achronological. Though it appears before the Sin of the Golden Calf, it actually was first commanded after, and in response to, the sin.
Chronological – Though Lekach Tov and R. Bachya agree that the building helped atone for the nation's error, they assert that the command, nonetheless, preceded the sin. God, in his mercy, provides a "cure" for "diseases" even before one gets sick.
Why now? According to these commentators, had the people not sinned, there would have been no need for the Mishkan. Once they erred, though, building a house for God was an essential part of their atonement process.18
No mention before ascending – According to the Sifre and Tanchuma, God only mentions that he will give Moshe the Tablets (and said nothing about the Tabernacle) since that is all that occurred on the mountain during the first ascent.19 It was only during the second ascent, after the sin, that Hashem directed Moshe to build the Mishkan.
Focal point –
"וְשָׁכַנְתִּי בְּתוֹכָם" – This verse describes the goal of the building, to have God return to the nation after their sin.
Altars for atonement – Since the Tabernacle was built to atone for the nation's sin, it is appropriate that it becomes the site of sacrificial offerings that bring atonement for other sins as well.
General Atonement
The Tabernacle was built as a vehicle through which people could atone for their sins, regardless of the sin of the Golden Calf.
Chronology – Though R. Yosef Bekhor Shor follows Chazal and assumes achronology in the command, this position could easily hold that the story is in its proper place. God commanded to build an edifice to facilitate the atonement process, unrelated to the nation's specific blunder with the Calf.
Why now? If one asserts achronology, then one might suggest that the major offense of the nation made it evident that a site for atonement was necessary. Alternatively, if one maintains chronology, one might suggest that soon after giving the initial laws, Hashem instituted a process for atoning when one transgresses them.
No mention before ascending –
Does Hashem need a house?
Why a house? – It is not clear why Hashem needed to institute a Tabernacle as a site for sacrifices rather than allowing individual altars.
Focal point – This approach views the altar rather than the ark as the focal point of the Mishkan.