Why Such Detailed Instructions?

As I was reading through Exodus 25-30, I was struck by the level of detail that God gives on the construction of the Tabernacle and the priestly garments. God doesn't just say "build me a temple worthy of my presence" - instead He gives precise dimensions and exact requirements - something that even a non-architect could figure out to some degree. Obviously there was still room for artistic interpretation, such as exactly what the cherubim would look like, but overall, God had a very precise idea of what he wanted.

So my question is: "Why?" Why does God care that acacia wood was used - instead of oak or cedar? Why does God take pains to list the 12 different precious stones that are to be attached to Aaron's breastplate - instead of allowing others such as diamonds or rubies? What is so important about the dimensions of the Tabernacle which, while large, are certainly not massive?

I have a feeling that some of the requirements are based on symbolism which has been mostly lost throughout the ages. But I think the overall message here is that God wanted the Israelites to know that this Tabernacle was His. He came up with the plans, he instructed the builders, and he gifted the people with the talents to accomplish it. The Israelites could never turn around later and claim that any of this was theirs. They certainly built it - but it was not their idea.

How does this relate to today? One example is salvation. No human can save themselves - it is only by the blood of Christ. Certainly we have to be an active participant in the salvation process: faith, confession, fruits, etc. But we cannot do it without the grace of God, and we would never know how to do it, if Christ had not come to earth and told us and showed us.