K’chol asher ani mar’eh os’cha, eis tavnis hamishkan v’eis tavnis kol keilov, v’chen ta’asu - like all that I show to you, the form of the Tabernacle and the form of all of its vessels, this is what you shall do (Shemos 25:9)
As has already been noted, the form of service as well as the vessels used in the Tabernacle and the Beis ha-Mikdash have obvious symbolic meanings that transcend their physicality. They are emplaced in the courtyard [the external mizbeach used for korbanot] or inside the kodesh [the menorah, shulchan, mizbeach hazahav (used for incense) or inside the kodesh hakodoshim [the aron] in specified places, covered in gold or copper et. al. as a means of imbuing them with a special aura and demonstrate their uniqueness. Generally, the commentaries agree that the shulchan represents Divine bounty that presents us with our sustenance, the menorah symbolizes the Divine wisdom manifested in the creation of this world, the mizbeach, G-d’s gift of teshuvah and atonement, and the aron - the crown jewel that is held separate and protected by a paroches - represents the gift of Torah, the manual that teaches us how to live in this world.
Kli Yakar notes that three of the internal vessels - the aron, the shulchan and the mizbeach hazahav had a zer zahav - a crown of gold - along their tops. He sees this as being symbolic of the three types of crowns - or leadership positions - that adorn klal Yisrael; the kesser kehunah - the crown of priesthood, the kesser meluchah - the crown of kingship and the kesser Torah - the crown of Torah. Despite this commonality, he notes that there was a disparity in the measurements of the vessels. The measurements in the aron were all partial or broken [it measured two and a half amos by one and a half by one and a half]. The measurements of the shulchan were both partial and whole [two amos by two amos by one and a half] while the measurements of the mizbeach were all whole [five amos by five amos by three].
He explains this phenomenon in the following manner: the measurements of the aron - representing the crown of Torah - were not whole, for one should never think that he has mastered all of Torah. On the other hand, the measurements of the mizbeach - representing kapparah - were whole, for when man returns wholeheartedly to G-d and is granted atonement for his shortcomings, G-d wipes his slate clean and there are no vestiges of his sins left. In regard to the shulchan however - representing parnasah - some amos were whole and some partial, for while man must appreciate that G-d has given him whatever he needs in this world, he is nevertheless given permission to seek more.
Interestingly, Kli Yakar does not discuss the fact that the menorah did not have a zer zahav even though it was an internal vessel. More intriguing is the fact that there are no measurements specified for the menorah even though there is a detailed account of the designs that were to be incorporated. Finally, why of all of the vessels used in the Mishkan and Beis ha-Mikdash is the menorah the only one that must be made mikshah achas - of a single mass of gold?
Perhaps all of these singular qualities of the menorah can be seen as being necessary elements for transmitting its true symbolism - the Divine wisdom manifested in this world. That wisdom is completely separate from man, who might comprehend parts of it but who can never use it to adorn himself. Man’s tzelem Elokim can give him the basic ability to recognize its existence, but no one can reach the plateau where chochmas Hashem becomes his crown. This might account for the reason why Moshe found it so difficult to construct [see midrash to parashas Vayekhel].
The Divine wisdom manifested in this world is immeasurable and cannot be quantified by amos - either partial or whole. Chazal spoke of G-d as being m’komo shel olam - the space within which this world exists - while it is impossible to think of this temporal world as being the space within which G-d exists. Thus, the dimensions of the menorah are not given and the only details provided are the adornments through which its light shines forth.