Albert Barnes Commentary Exodus 38:8

"And he made the laver of brass, and the base thereof of brass, of the mirrors of the ministering women that ministered at the door of the tent of meeting." — Exodus 38:8 (ASV)

See the marginal reference. The women who assembled at the entrance of the tent of meeting were most probably devout women who loved the public service of religion. The giving up of their mirrors for the use of the sanctuary was a fit sacrifice for such women to make (Compare to Exodus 35:22 note).