In the seventh aliyah Betzalel makes the altar of the burnt offerings. He makes the wash basin out of copper, from the mirrors of the women. At first, Moshe didn't want to use these mirrors because they represented the women's vanity in adorning themselves, but G-d treasured them more than anything else because the women used these mirrors to attract their husbands when they were fatigued in their slavery in Egypt. These lavers were to be used in the Sotah ceremony to make peace between a husband and wife. The Alter Rebbe - Rabbi Schneur Zalman of Liadi explains that the offerings for the Mishkan included gold, silver, and copper, but nothing sparkled except for the mirrors presented by the women.
Although, these lavers were the last articles of the Mishkan to be made, they were nonetheless the first articles to be used at the starting of every sanctuary service for the washing of the Kohanim.
