Why was God so specific about how to make the Tabernacle? The Book of Exodus (ch 25–27) spends quite a bit of time describing how to build the Tabernacle, right down to the type of metal and wood to use for minor parts, all straight from the mouth of God.  Why did God go into such great detail about seemingly trivial matters?  Besides the obvious reason of, "It was important," what reasons have published Christian commentaries suggested for the amount of text devoted to a physical description of the Tabernacle?
A number of different answers to this question have been given by Christians through history.  Broadly speaking, the reasons for the extensive detail given by Moses might be categorized as follows: (1) to foreshadow future events and entities, (2) to demonstrate the importance of religious worship, and (3) to display God's glory.
Foreshadowing
Christians widely recognize, based on passages Hebrews 9, that some aspects of the tabernacle are types of New Testament realities. However, from the days of the church fathers, many have attempted to seek out a spiritual interpretation or foreshadowing for every detail of the Tabernacle.  Gregory the Great, for example, sees the Ark of the Covenant's features as significant:

What but the holy Church is figured by the ark? To which four rings of gold in the four corners are ordered to be adjoined, because, in that it is thus extended towards the four quarters of the globe, it is declared undoubtedly to be equipped for journeying with the four books of the holy Gospel.1

Similarly, the two cherubim, Gregory says, signify &quot;the two testaments,&quot; since the word means &quot;fullness of knowledge.&quot;2
Examples of this sort of interpretation apparently abounded in the early church, since Origen, no stranger to allegorical exegesis, warned about some who go too far:

When the (description of the) fitting out of the tabernacle is read, believing that what is written is a type, they seek to adapt what they can to each particular related about the tabernacle,— not being wrong so far as regards their belief that the tabernacle is a type of something, but erring sometimes in adapting the description of that of which the tabernacle is a type, to some special thing in a manner worthy of Scripture.3

Importance of worship
Some argue that the level of detail here is an indication of the importance of worship to God.  Matthew Henry contrasts the amount of detail mentioned in the Creation account:

He that gave us no account of the lines and circles of the globe, the diameter of the earth, or the height and magnitude of the stars, has told us particularly the measure of every board and curtain of the tabernacle; for God’s church and instituted religion are more precious to him and more considerable than all the rest of the world.4

Matthew Poole reasons that the additional detail was necessary here because man on his own could not deduce what was necessary to properly worship God:

the light of reason implanted in all men, gives him greater help in the discovery of moral and judicial things than in ceremonial matters, or in the external way and manner of God’s worship; which is a thing depending wholly upon God’s institution, and not left to man’s invention, which is a very incompetent judge of those things, as appears from hence, because the wittiest men, destitute of God’s revelation, have been guilty of most foolery in their devices of God’s worship.5

God's glory
A third explanation is that the detailed instructions ensured that the tabernacle best displayed God's glory.  Coffman writes:

Despite the fact of the tabernacle, where God would dwell (in a figure) with his people, being in essence a portable tent with an enclosure about it, its holiness was emphasized in the fact that only the choicest materials were to be used in its construction.6

Keil and Delitzsch argue that the specifics had to come from God, not man:

If the sanctuary was to answer its purpose, the erection of it could not be left to the inventive faculty of any man whatever, but must proceed from Him, who was there to manifest Himself to the nation, as the Holy One, in righteousness and grace.7

Young likewise sees the completed tabernacle as something that would cause the world to praise God:

These Israelites, when all was finished according to the pattern in the mount, had then something to show which would make an impression on men of the right sort in the outside world. Here was an answer to the question, &quot;Where is now your God?&quot; Visible he himself is not; but here is a dwelling-place not in anything constructed after art and man's device, but entirely of Divine direction. All our institutions are nothing unless we can trace them to the inspiration and control of God.8

Summary
Different Christians will tend to emphasize one or another of these views, at the expense of the others, but it seems likely that there is some truth to each of them.  Christians can usually agree that the tabernacle points to Christ, and that it indicates the importance of the worship and glory of God.

References

Pastoral Care 2.11
Homily 25
First Principles, Book 4
Complete Commentary
Annotations
Commentaries
Commentary
Pulpit Commentaries