Parshat Ki Tisa
In 30:18 It says, "And you should make the basin (for washing) from copper".
All the vessels in the mikdash were made from gold. Why is the washing basin the exception? Why copper?
The Seforno asks why this vessel is mentioned here at the beginning of Ki Tisa when all the other vessels were mentioned in Teruma (and a couple in Tetzaveh)?
The Seforno explains that this vessel, the washing basin, did not have the purpose of effecting Divine Presence in the Mishkan, as did all the other vessels. The basin was simply for the Kohanim to be able to prepare for the service. It was functional. Therefore, it is not mentioned with the others - because it has a different purpose.
This idea also answers my question.. The basin did not have the same purpose as the others.
The other vessels all had to made of gold because they were effecting השראת השכינה - Divine Presence. We know "there is no destitution int he place of wealth" which is why they had to be very strict about not using broken vessels, using only gold, etc.. so as not to give the appearance of any level of "עניות" - because in the process of effecting the Divine Presence, a certain level of כבוד was needed, and that required the vessels to be made of gold.
Yet the basin did not have that as its purpose. The basin was simply functional. It was not there for glory and respect. They simply had to wash their hands and feet. To do that, the basin did not have to be gold.