A quick pre-Shabbos thought on parshah Terumah:
Sforno comments on the phrase "So that I may dwell among them..." by noting that the zenith of the tabernacle was the ark and its cover. Specifically, he suggests that the reason the cherubim faces were turned downards toward the ark was to remind us that the klal's focus is always on the contents of the ark, namely Torah and by extension, Hashem.
To that end, I found it fitting that the discussion of the tabernacle emphasizes that the design thereof was not extravagant, simply suitably ornate for its contents. I would suggest, in turn, that this degree of ornamentation is similar in its meaning to the difference in the garb of the regular kohanim versus the kohen gadol. Regular kohanim, as we know, wore simple linen garments; these garments were clean and attractive. However the kohen gadol's additional splendour was not for his glory, but rather a reflection of his role as the party who entered the Holy of Holies, i.e., this splendour was fitting because he was the one kohen who stood before the shechina. Moreover, it was due to this role that the additional garments and ornamentation had a practical role spiritually- they served as the conduit for Hashem to answer the kohen's questions, for example, in the case of the choshen mishpat.
And so we learn that just as a commoner will dress "down" every day as opposed to the day on which he is presented to the King, so too the regular kohanim dressed. As the representative of the nation who bore the responsibility of presenting himself to the shechinah, the kohen gadol was dressed suitably for one who stood before the King. By extension, we learn that as we grow in Torah, we must dress accordingly, in a manner that demonstrates the fact that, in galus, we stand before Hashem always.