Marot ha-Tzovot: Reflections of Male and Female, Lens of Prophecy
Mirrors have occupied an interesting place in human thought. More than just a means of seeing the self, they are often an archetype for a portal between mortal and immortal realms, or ironically, a means to see "beyond" the self ("Mirror, mirror on the wall, whose the fairest of them all?" is followed by the power to see unseen and distant things).
Given that the Tabernacle and Temple were the places of divine vision and encounter, places to "see the face of the Eternal (Deut. 16:16; Ps. 11)," it is surprising that more early interpreters of the Torah didn't make symbolic hay out of Exodus 38:8, an explicit reference to mirrors associated with the sanctuary of God:
He made the laver of copper and its stands of copper, from the mirrors of the women who worked at the opening of the Tent of Meeting.
The laver of copper/bronze used in the Mishkan came from these mirrors, making them "integral" to the cosmic scheme embodied in the Sanctuary and its objects. But in what way?
In a small number of Rabbinic interpretations, these mirrors were not symbols of divine vision, but emblems of female sexuality and the Sages explored its appropriateness both in the sanctuary as the locus of God's holiness and in the larger divine plan. In Numbers Rabbah, Moses selects them specifically because the Israelite women did not use them for "immorality" (i.e., used them to make themselves look more sexually appealing) (IX:14). RaSHI playfully tweeks this rather puritan Midrash by making Moses' prudishness a foil for a more positive view of sexuality:
From the mirrors [marot] – The Israelite women had in their possession mirrors that they would look in when they put on their jewelry. Even these mirrors they did not withhold from the donations to the Tabernacle, and Moses was disgusted with them because the mirrors were made for the evil inclination. God said to [Moses], "Accept the mirrors, for they are more precious to Me than anything else, since with the mirrors the women brought many hosts of children into being." When their husbands were oppressed with slave labor, the women would go and bring them food and drinks, and feed them. They would bring the mirrors with them and each one of the women would look at herself in the mirror with her husband and entice him with worlds, saying "I am more beautiful than you." From this they would make their husbands desirous and have sex, and the women became pregnant there (in the fields), as it says: "Under the apple tree I roused you" (Song of Songs 8:5). And this is why [it calls them] "marot tzovot" which can be read as "mirrors of multitudes." (Tanhuma Pikudei 9 has a similar account)
Kabbalah, by contrast, focuses on the word-play of the word marah between "mirror" and "vision." Thus Marot ha-Tzovot can be read as "visions/mirrors of the Hosts [of heaven]," reminiscent of another esoteric teaching, the "nine shining speculum," or levels of prophetic vision (Num. 11:6-8; T.B. Yebamot 49b). Thus these "mirrors" associated with the place of Divine Presence (the lowest of the sefirot which is the "speculum that does not shine") are apertures for gazing upon degrees of divine light, as Joseph Gikatilla (13th Cent) wrote:
Know that Moses our teacher was greater than all the other prophets, and Moses never used the phrase "YHVH TZVAOT" for his level cleaved to YHVH [alone] and he did not have to look into "mirrors of TZoVOT" (the hosts or legions of women). Thus it is written that Moses our teacher, PBUH, looked into the luminous mirror (Num. 12:8). The other prophets see through an opaque, unfinished mirror "...I make myself know to him in a vision [Marea] (Hosea 12:11)" [which] is the essence of Marot Tzovot...this is also the essence of the mirrors of Tzovot that were arrayed around the doorway of the Tent of Meeting. 
In later sources, the tenth sephirah, Malchut/Shekhinah, is even dubbed the Marot ha-Tzovot. By the late 13th Century there is a book devoted entirely to the Kabbalistic symbolism of these "mirrors"  Which is not to say that the sexual association of the marot made by the Rabbis is lost - Kabbalah takes as a premise that God's creation is shot through and sustained at all levels by erotic energy. Elsewhere Gikatilla links the mirrors of Exodus 38:8 to the lower sefirot of Hod (female) and Netzach (male), which are most closely tied to prophecy.
Zal g'mor - To learn more consult the Encyclopedia of Jewish Myth, Magic, and Mysticism: http://www.amazon.com/Encyclopedia-Jewish-Myth-Magic-Mysticism/dp/0738709050
1. Weinstein, Avi, trans., Gates of Light, Harper Collins, 1994, p. 119
2. Matt, Dan, "David ben Yehudah HeHasid and His Book of Mirrors," HUCA Annual, 1980.