Among the various items used to build the Mishkan, the verse tells us that our ancestors used something called "tachash skins" for the outer covering of the Mishkan and as a slipcover for the holy vessels while they traveled in the desert. The exact identity of the tachash has been a matter of great speculation. Some say it was a (reddish or violet) dye used to color skins or cloth in the Mishkan, but most say it was an animal. Which one? Among the opinions: Ermine, badger, a one-horned animal called a keresh; an antelope, giraffe, the narwhal (whose left tooth developed into a single horn-like appendage); the sea cow or seal, okapi or zebra. Most say it was a non-kosher animal, but others (Rav Moshe Sofer) say it was miraculously made kosher just for use in the Mishkan. The Lubavitcher Rebbe explains that the uniqueness of the tachash is that it is the only creation that was used exclusively for holy purposes. Thus, the tachash illustrates that the ultimate purpose for all of creation is to be used only in service of Hashem. This will be fully realized with the building of the Third Temple, may it be speedily in our days!
Beit Midrash Torah Portion and Tanach Vayakhel