(17) The Lord spoke to Moses, saying:
(18) Make a laver of copper and a stand of copper for it, for washing; and place it between the Tent of Meeting and the altar. Put water in it,
(19) and let Aaron and his sons wash their hands and feet [in water drawn] from it.
(20) When they enter the Tent of Meeting they shall wash with water, that they may not die; or when they approach the altar to serve, to turn into smoke an offering by fire to the Lord,
(21) they shall wash their hands and feet, that they may not die. It shall be a law for all time for them — for him and his offspring — throughout the ages.
(18) Make a laver of copper … for washing: Real life is imperfect, and no mortal is completely free of pollution. The laver emphasizes the need for purification before entering the Temple and participating in its service.
A laver of copper: The laver was like a large cauldron with spouts, from which the water flowed.
And a stand of copper for it: As already noted, three metals were used in the Tabernacle: (1) Gold, a symbol of moral human qualities, gave the Tabernacle much of its magnificence. (2) Silver, representing the material and economic aspects of life, was used in the foundations of the walls and pillars of the Tabernacle. (3) Copper, symbolic of human passions, was a key element in those Tabernacle features that served to prepare the visitor for entry.
Copper bears a certain resemblance to gold, but it is not gold. Likewise, human passions only pretend to be moral. The laver represents the purification (but not the destruction!) of passions, which allows the creative energy of human passions to be channeled in a positive direction.
Linguistically, copper, nechoshet, is closely related to nachash, “serpent”. Under the influence of his passions a person is unable to distinguish between right and wrong, between good and bad. That is the influence of the serpent in the Garden of Eden. The purifying waters dispensed from the copper laver represent the cleansing of a person from those mistakes committed when, driven by his passions, he has mistaken falsehood for truth.
(19) And let Aaron and his sons wash their hands and feet [in water drawn] from it: The priests performed the Temple service unshod.
Because the body’s extremities continuously come in contact with the outside world, in which evil abounds, they must be cleansed before performing the Temple service. The requirement to wash one’s hands before partaking of a meal derives from this same connection, because the table on which a person eats is likened to an altar, and each meal is likened to a sacrifice (the custom of putting salt on bread at every meal is likewise based on this connection: Salt was an essential element in the Temple offerings. “You shall season your every offering of meal with salt; you shall not omit from your meal offering the salt of your covenant with God; with all your offerings you must offer salt.” – Lev. 2:13).
(20) When they enter the Tent of Meeting they shall wash with water, that they may not die; or when they approach the altar to serve, to turn into smoke an offering by fire to the Lord: The Temple service, like any service, requires proper preliminary preparation, or it can result in death. A practical example of this is an electrician who makes bodily contact with a high-voltage source without suitable preparation and equipment.
(21) They shall wash their hands and feet, that they may not die. It shall be a law for all time for them — for him and his offspring — throughout the ages: The commandment is repeated to emphasize that it applies not only to Aaron himself and his sons, but to all successive generations. Cleansing the priests from impurities is necessary not only when the Temple service is first initiated; it remains an essential element of the Temple’s functions for all time.
 This connection between nachash, “serpent,” and nechoshet “copper,” is especially evident in the story of the copper serpent, see Num. 21:9.