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 Exodus 35:22 note).

He made the laver - See Clarke's note on Exodus 30:18, etc.
The looking-glasses - The word מראת maroth, from ראה raah, he saw, signifies reflectors or mirrors of any kind. Here metal, highly polished, must certainly be meant, as glass was not yet in use; and had it even been in use, we are sure that looking - Glasses could not make a Brazen laver. The word therefore should be rendered mirrors, not looking-glasses, which in the above verse is perfectly absurd, because from those maroth the brazen laver was made. The first mirrors known among men were the clear, still, fountain, and unruffled lake; and probably the mineral called mica, which is a very general substance through all parts of the earth. Plates of it have been found of three feet square, and it is so extremely divisible into laminae, that it has been divided into plates so thin as to be only the three hundred thousandth part of an inch. A plate of this forms an excellent mirror when any thing black is attached to the opposite side. A plate of this mineral, nine inches by eight, now lies before me; a piece of black cloth, or any other black substance, at the back, converts it into a good mirror; or it would serve as it is for a square of glass, as every object is clearly perceivable through it. It is used in Russian ships of war, instead of glass, for windows. The first artificial mirrors were apparently made of brass, afterwards of polished steel, and when luxury increased they were made of silver; but they were made at a very early period of mixed metal, particularly of tin and copper, the best of which, as Pliny tells us, were formerly manufactured at Brundusium: Optima apud majores fuerant Brundisina, stanno et aere mixtis - Hist. Nat. lib. xxxiii., cap. 9. But, according to him, the most esteemed were those made of tin; and he says that silver mirrors became so common that even the servant girls used them: Specula (ex stanno) laudatissima Brundisii temperabantur; donec argenteis uti caepere et ancillae; lib. xxxiv., cap. 17. When the Egyptian women went to the temples, they always carried their mirrors with them. The Israelitish women probably did the same, and Dr. Shaw states that the Arabian women carry them constantly hung at their breasts. It is worthy of remark, that at first these women freely gave up their ornaments for this important service, and now give their very mirrors, probably as being of little farther service, seeing they had already given up the principal decorations of their persons. Woman has been invidiously defined by Aristotle, an animal fond of dress, (though this belongs to the whole human race, and not exclusively to woman). Had this been true of the Israelitish women, in the present case we must say they nobly sacrificed their incentives to pride to the service of their God. Woman, go thou and do likewise.
Of the women - which assembled at the door - What the employment of these women was at the door of the tabernacle, is not easily known. Some think they assembled there for purposes of devotion. Others, that they kept watch there during the night; and this is the most probable opinion, for they appear to have been in the same employment as those who assembled at the door of the tabernacle of the congregation in the days of Samuel, who were abused by the sons of the high priest Eli, 1-Samuel 2:22. Among the ancients women were generally employed in the office of porters or doorkeepers. Such were employed about the house of the high priest in our Lord's time; for a woman is actually represented as keeping the door of the palace of the high priest, John 18:17 : Then saith the Damsel that Kept The Door unto Peter; see also Matthew 26:69. In 2-Samuel 4:6, both the Septuagint and Vulgate make a woman porter or doorkeeper to Ishbosheth. Aristophanes mentions them in the same office, and calls them Σηκις, Sekis, which seems to signify a common maid-servant. Aristoph, in Vespis, ver. 768: -
Ὁτι την θυραν ανεῳξεν ἡ Σηκις λαθρα.
Homer, Odyss., ψ, ver. 225-229, mentions Actoris, Penelope's maid, whose office it was to keep the door of her chamber: -
Ακτορις - - -
Ἡ νωΐν ειρυτο θυρας πυκινου θαλαμοιο.
And Euripides, in Troad., ver. 197, brings in Hecuba, complaining that she who was wont to sit upon a throne is now reduced to the miserable necessity of becoming a doorkeeper or a nurse, in order to get a morsel of bread.
- - - η ταν
Παρα προθυροις φυλακαν κατεχουσα,
Η παιδων θρεπτειρα.
Sir John Chardin observes, that women are employed to keep the gate of the palace of the Persian kings. Plautus, Curcul., act 1, scene 1, mentions an old woman, who was keeper of the gate.
Anus hic solet cubitare, custos janitrix.
Many other examples might be produced. It is therefore very likely that the persons mentioned here, and in 1-Samuel 2:22, were the women who guarded the tabernacle; and that they regularly relieved each other, a troop or company regularly keeping watch: and indeed this seems to be implied in the original, צבאו tsabeu, they came by troops; and these troops successively consecrated their mirrors to the service of the tabernacle. See Calmet on John 18:16.

And he made the laver [of] brass, and the foot of it [of] brass, of the (b) lookingglasses of [the women] assembling, which assembled [at] the door of the tabernacle of the congregation.
(b) R. Kimbi says that the women brought their looking glasses, which were of brass or fine metal, and offered them freely for the use of the tabernacle: which was a bright thing and of great majesty.

And he made the laver of brass, and the foot of it of brass,.... Not of the brass of the offering, for of that were made the brazen altar, its grate and vessels, the sockets of the court and court gate, and the pins of the tabernacle, Exodus 38:29 but no mention is made there of the laver; for that was made, as here said:
of the looking glasses of the women assembling, which assembled at the door of the tabernacle of the congregation; though these are called looking glasses, it is not to be supposed that they were made of glass as ours are; for of what use could such be in the making of a brazen laver? Some indeed choose to read the words "with the looking glasses" (d), and take the sense to be, that there were looking glasses about the laver, affixed to it, that when the priests came to wash, they might see their spots, and the better know how to cleanse themselves from them: but it should be observed, that the priests did not come hither to wash their faces, but their hands and feet, Exodus 30:19 and so stood in no need of looking glasses for that purpose. The particle is here, as Aben Ezra observes, instead of and denotes the matter of which the laver was made, and therefore these instruments to behold the face in, or those mirrors, were of brass, as both he and Philo the Jew (e) affirm; and, indeed, what else could they be, for a laver of brass to be made of? mirrors in former times were made of various sorts of metal polished, some of gold, some of silver, some of brass, and some of brass and tin (f); and the Indians to this day have mirrors made of brass, well polished, and exactly represent the complexion (g). Pliny says (h), that those of Brundusium, which were made of brass and tin mixed, were with the ancient Romans reckoned the best. Aristotle (i) speaks of mirrors of brass, and of their receiving and showing the least touch, because the brass is smooth and polished; and so in our times, there are such as are made of polished steel, and even of burnished brass too: De la Hay (k) says that he had one in his study, which was given him, made of brass of Damascus, and was so finely polished that no crystal one could give a truer sight of the face than that; however, it is certain the ancients used such kind of mirrors; see Job 37:18 these the good women of Israel, in their great zeal, brought for the service of the sanctuary, though they were of daily use, and peculiarly serviceable to them in their dressing; for though the word "women" is not in the text, it is rightly supplied, as it is in all the three Targums, the word being feminine, and as may be justified by a parallel passage, 1-Samuel 2:22 indeed Varenius (l) proposes another, rendering the words thus,"of the looking glasses in great number gathered together, which they had heaped together at the door of the tabernacle of the congregation;''but the word used is active and not passive, and is used of persons gathering together, and not of things gathered, as appears from the above quoted place, and others; and these women gathered together, not for devotion and religion, to pray, as the Targums of Onkelos and Jonathan paraphrase it, or to pray, and hear the words of the law, as Aben Ezra, much less to bear any part in the ministry and service of the sanctuary, which as yet was not built; for this tabernacle of the congregation was no other than the tent of Moses, or, however, some little tabernacle erected while the other was preparing, see Exodus 33:7 hither the women crowded with their mirrors of brass for the service of the sanctuary; for the word signifies an assembling in troops like an army; and they came in great numbers and beset the door of the tent where Moses was, that he might take their offerings at their hands; not but that it will be allowed that devout women sometimes did assemble at the tabernacle and temple, to perform acts of religion and devotion; but this seems not to be the case here, nor this a time and place for it; see 1-Samuel 2:22.
(d) "cum speculis", Oleaster. (e) De Vita Mosis, l. 3. p. 673. (f) Vid. Doughtei Analecta Sacr. excurs. 44. p. 124. (g) Agreement of Customs between the East Indians and Jews, art. 15. p. 65. (h) Nat. Hist. l. 33. c. 9. & l. 34. c. 17. (i) De Insomniis, c. 2. (k) Apud Habikhorst. de mulier. Zobheoth in Thesaur. Theolog. Philolog. vol. 1. p. 321. (l) Apud ib. p. 318.

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 (Luke 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].

This laver signified the provision that is made in the gospel for cleansing our souls from the pollution of sin by the merit of Christ, that we may be fit to serve the holy God in holy duties. This is here said to be made of the looking - glasses of the women that assembled at the door of the tabernacle. It should seem these women were eminent for devotion, attending more constantly at the place of public worship than others, and notice is here taken of it to their honour. These looking - glasses were of the finest brass, burnished for that purpose. In the laver, either they were artfully joined together, or else molten down and cast anew; but it is probable the laver was so brightly burnished that the sides of it still served for looking - glasses, that the priests when they came to wash might there see their faces, and so discover the spots to wash them clean.