The peculiar blue [תכלת, tekhelet] thread used in tzitzit [ritual fringes] (Numbers 15:37-41) also appears prominently in the construction of Tabernacle (Exodus 25ff). It is used in the inner curtains and the loops that connect them; it also appears throughout the priestly vestments.
Why this blue?
It has been taught: R. Meir used to say: Why is blue [תכלת] specified from all the varieties of colours? Because blue resembles [the colour of] the sea, and the sea resembles [the colour of] heaven, and heaven resembles [the colour of] the Throne of Glory, as it is said: And they saw the God of Israel and there was under His feet as it were a paved work of sapphire stone [לבנת הספיר], and as it were the very heaven for clearness (Exod. 24:10) and it is written: The likeness of a throne as the appearance of a sapphire stone [אֶבֶן-סַפִּיר] (Ezek 1:26).
— Sotah 17a (also: Menachot 43b and Chullin 89a)
Kedushat Levi links the above passage about blue, תכלת, to the stages of a creative act, beginning and ending with its purpose [תכלית]:
[A project from thought to completion] has undergone four distinct stages. 1) original mental image of the project; 2) clarification of the details, etc. 3) translating thought into deed. 4) carrying out the intention which originally prompted the project. [Punctuation follows translation.] When the original mental image of the project is seen reflected after its successful completion, the person inhabiting this building will experience a sense of satisfaction and joy.
— Kedushat Levi, p. 475 (see Source Materials for full citation)
One of the 30-cubit, goat-hair curtains on the outside of the Tabernacle is folded over the front of the tent (Exodus 26:9; see Thirty Cubits and Cloaking) for more on the curtains). Two aspects of this are emphasized in the commentary of Kedushat Levi, among others:
Folding: Folding [כפל, khaphal] is related to the idea of “klipah” [קלפה], the protective shell covering God’s Light in the world, according to mystical teaching. Kedushat Levi links the folding of the curtain and God’s cloaking, to protect humans from what they cannot withstand, adding that “folding over” implies reinforcing something not otherwise as strong as necessary. (Kedushat Levi, p. 473; full citations for Kedushat Levi, Stone Chumash in Source Materials.)
Half: Kedushat Levi also emphasizes the fact that the curtain is folded in half. He links “half” to “awe” through a play on the Hebrew words: the curtain, folded in “half” [חצי, chatzi], is linked via “crush” [מחץ, machatz] to “awe.” (More below.)
Additional thoughts on the concept of “half,” regarding the command to collect a half-shekel as part of the census embedded in the Tabernacle story, suggest a different direction:
Many commentators interpret homelitically that the requirement of half a coin alludes to the concept that no Jew is complete unless he joins with others; as long as we are in isolation, each of us is only “half” of our full potential.
— Stone Chumash, on Exodus 30:13
Combining these views on folding and half seem to suggest that any approach to God is best accomplished in community.
Readers of Moby Dick have long skimmed the whaling sections. Love-story followers generally hurry through the “war” part of War and Peace, while others skip through the boring relationship stuff to focus on land distribution. Likewise, many Bible readers’ eyes glaze over at the close of Exodus: Some 200+ Torah verses describe plans for the Tabernacle and its furnishings. Another 200+ verses describe the actual work. Four entire weekly Torah readings are dedicated to the details of the Tabernacle, with Ki Tisa’s story of the Golden Calf in between.
Some teachers focus on general messages extracted from these passages: the importance of working collaboratively, supporting community infrastructure, or honoring the arts, for example. But others take an allegorical view, mining details rather than glossing over them. Kedushat Levi (Rabbi Levi Yitzchak of Berditchev, 1740 – 1809) is one of the later. And some of those details surround the number 30.
The inside of the Tabernacle, the desert worship space of the Israelites, is 30 cubits long. (This is worked out from directions for various components, described in Exodus 26-27.) An inside covering is composed of ten panels of “twisted linen, and indigo and purple and crimson, with cherubim, designer’s work,” each measuring 28 cubits by 4 cubits (Alter’s translation; citation below). Eleven goat-hair panels of 30 cubits by 4 cubits create an additional covering over the whole construction. (Explicit instructions in Exodus 26:1 and 26:7).
The inside coverings are joined so “that the Tabernacle be one whole” (Exodus 26:6).
26:6) that the Tabernacle be one whole
This phrase leads Abraham ibn Ezra to muse over how unity in the greater world is constituted by an interlocking of constituent parts that become a transcendent whole, as in the unity of microcosm and macrocosm. One need not read this section homelitically, as he does, in order to see the power of summation of this particular phrase.
— Alter, Robert. The Five Books of Moses: A Translation with Commentary. (NY: Norton, 2004)