The Torah (38;8) states: "He made the Kiyyor of copper and its pedestal of copper, with the mirrors of the women who congregated at the entrance of the Tent of Meeting."
Rashi (38;8) relates: "The daughters of Israel had in their possession copper mirrors which they would look into when they would beautify themselves. Even those mirrors they did not withhold from bringing for the contribution toward the Mishkan. But Moshe rejected them because they were made for accomplishing the ends of the Evil Inclination. The Holy One, Blessed is He, said: "Accept them, because these are the dearest to Me of all, for by means of them, the women established many legions of offspring in Egypt." When their husbands would be exhausted by the racking labor imposed on them by the Egyptians, they would go and bring them food ad drink, and feed them. Then they would take the mirrors, and each one would view herself with her husband in the mirror and entice him with words, saying, "I am handsomer than you."
Firstly, why did Moshe think he shouldn't accept the mirrors? Certainly he knew that they were used to help the nation multiply and that should override the fact that they created lust!?!
Additionally, why did Hashem consider these mirrors more precious than all the other gifts of the Mishkan? Why didn't He simply say they were "acceptable" for the Mishkan?
Rabbi Yochanan Zweig explains that the men of the nation of Israel were feeling down about themselves and their libido's were crushed. And why is that? The Gemara (Sotah, 11b) explains that the words "racking labor" mean that in Egypt the men did women's work and vice versa. As a result, the men began to feel like they were the woman in the house. Therefore, Hashem created the mirrors to make them feel better. And how did these mirrors raise up the spirits of the men? Rashi explains: "They would take the mirrors and each one would view herself with her husband in the mirror and entice him with words, saying "I am handsomer than you." Meaning, the women would take the mirrors and tell their husbands that they are still the man in the house (for the women were still more beautiful), despite their womanlike occupation. This would give the men a "new identity" and revive their feelings of being the man in their home.
We can now answer our questions...
Moshe thought that the mirrors were simply for beautifying (for the women would "look into when they would beautify themselves"). Hashem therefore responded that the main purpose of the mirrors was to give the men a new identity (this was accomplished by each women looking into the mirror with her husband and saying, "I am handsomer than you"), for they felt like women because they were doing womanlike labor. Thus, the mirrors weren't a matter of lust. Rather, they were a matter of finding one's self--one's role (Husband vs. Wife). For this same reason, Hashem said that the mirrors were the dearest to Him of all the gifts of the Mishkan-because by giving back the men their self identity their libido's were revived and that helped the nation multiply.
Rabbi Yochanan Zweig explains further that we could learn out a very important lesson regarding "shalom bayis" (meaning: "peace in the home") from here. Rashi (38;8) explains later that the Kiyyor was made from the the mirrors because its purpose was to make peace between man and wife. How did the Kiyyor make peace between man and wife? Rabbi Yochanan Zweig explains that the foundation of shalom bayous is that man and wife should each know their role in the house. And why is that? Rabbi Zweig explains that almost all issues of controversy between man and wife stem from control issues, for each person doesn't understand their role in the marriage. The mirrors therefore came and gave them a clear picture that despite their occupations, the man was still the man of the house and visa versa. Husband and wife each need to understand what their role in the marriage is and that will be the vehicle for shalom bayis.
Rabbi Yochanan Zweig therefore explains that husband and wife shouldn't love each other for their job or appearance--rather, they should love each other for the people they are. This is exactly what the women were telling the men--By looking in the mirror and telling the men, "I am handsomer than you" the women were saying to their husbands that despite their womanlike occupation and inferior appearance, they still loved them. Thus, we should all appreciate our spouses' for the people they are and verbalize it the way the women would when we were enslaved in Egypt.
Summary: Rashi (38;8) relates that Moshe didn't accept the copper mirrors from the women to be part of the mishkan because the women used them to beautify themselves which then led to lust. Hashem, however, said to accept them for they helped the nation multiply in Egypt. However, surely Moshe knew that the fact that the mirrors helped the nation multiply should override the their lead to lust? Why did he think they should not be accepted? Rabbi Yochanan Zweig explains that Moshe thought that the main purpose of the mirrors were for the women to beautify themselves. Hashem therefore responded that the women would look in the mirror with their husband and say "I am handsomer than you." What's the meaning of that? Rabbi Zweig explains that in Egypt the men would perform women's work and visa versa. As a result, the men's libido's were crushed. However, when their wives would look into the mirror with them and tell them they're prettier they were in effect telling their husbands that they're still the man of the house. Thus, the mirrors gave the men a "new identity."