Jamieson, Fausset and Brown on Exodus 38:8

8. laver of brass ... of the looking glasses of the women--The word mirrors should have been used, as those implements, usually round, inserted into a handle of wood, stone, or metal, were made of brass, silver, or bronze, highly polished [Wilkinson]. It was customary for the Egyptian women to carry mirrors with them to the temples; and whether by taking the looking glasses of the Hebrew women Moses designed to put it out of their power to follow a similar practice at the tabernacle, or whether the supply of brass from other sources in the camp was exhausted, it is interesting to learn how zealously and to a vast extent they surrendered those valued accompaniments of the female toilet.

of the women assembling ... at the door--not priestesses but women of pious character and influence, who frequented the courts of the sacred building (Lu 2:37), and whose parting with their mirrors, like the cutting the hair of the Nazarites, was their renouncing the world for a season [Hengstenberg].