The three metals used in the Mishkan – gold, silver and brass – are frequently treated together. Chazal inform us that the use of these metals corresponded to the Avot:
Gold – this refers to Avraham, who was refined in the fiery furnace like gold.
Silver – this refers to Yitzhak who was smelted like silver on the altar.
Brass – this refers to Yaakov, as it says: I have divined that God has blessed me because of you. (Shemot Rabbah 49:2)
We perceive the Mishkan as the focal point of Jewish life – in some way, the physical culmination of the spiritual goals that have been set for us. In that sense, the Mishkan reflects all the accomplishments of the Jewish people, whose identity was established by the Avot. Avraham, Yitzhak and Yaakov invested the nation with all the qualities it would need to fulfil its mission and as such, each was well represented in the construction of the Mishkan, the apogee of their achievements. The Ramban expands on this theme in his introduction to the book of Shemot:
Scripture has concluded the Book of B’Reishis, which is the book of creation, about the genesis of the world, the formation of everything and the events of the [lives of the] Avot, the progenitors of their descendents…. The exile [in Egypt] was not concluded until the day on which they returned to their place and to the level of their Avot. When they came out from Egypt, although they had departed the house of slavery, they were still considered exiles, as they were in a land that was not theirs, wandering in the desert. But when they came to Mount Sinai, made the Mishkan, and God once again rested His presence among them, then they returned to the level of their Avot…. Only then they were considered redeemed; hence this book finishes with the conclusion of the subject of the Mishkan and with the glory of God continuously filling it.
It seems that the use of the three metals in the Mishkan was a realisation of the talents and input of the Avot in the development of the Jewish nation.
Rav Hirsch also addresses the conceptual reasons for including metals in the manufacture of the Mishkan. He notes that Scripture uses metals metaphorically in three contexts: with reference to their density, value and metallurgical properties. Nechoshet (brass) is principally that is used to denote rigidity and obstinacy, although in general, it is used to indicate the qualities of firmness and strength. Gold and silver, on the other hand, are used to denote value. However, metals are most often used as metaphors for purity, endurance and refinement. As Rav Hirsch explains:
The more precious metals are found in a pure, unalloyed state but often with mixtures of non-precious ores and residues. Yet, even in this impure state, such metals can be refined. The refining process, in which the pure is separated from non-precious and non-recoverable metals, is affected by means of fire. Moreover, alloys of precious and non-precious metals produce manifold grades of purity and impurity, ranging full cycle from the original state of perfect purity to an equal degree of purity regained by and after repeated refinings. The intermediate degrees of purity can be determined by tests and experiments, but even in the poorest mixture, the smallest granule of precious metal is not lost but can be recovered. Finally, the capability of a precious metal to endure is in direct proportion to its preciousness and purity, and the purest and most precious gold is also that which offers the most lasting resistance to the corroding action of time and the elements. Thus, metals represent the best symbols for all things good and true in every mixture with elements of evil and falsehood. The concepts of purity, impurity and fineness in metals need only be taken in their symbolic meaning to express the best in ethics and moral truths…. It is clear from all the passages that in each case the metals are used as symbols characterising varying degrees of moral purity and truth. While n’choshes represents an impure metal, still unrefined, silver and gold represent varying degrees of purity, moral nobility and constancy. (Collected Writings of Rabbi Samson Raphael Hirsch vol. 3)
Rav Hirsch further observes that while gold is usually found in a pure state and can withstand the most rigorous tests, silver requires smelting and must always be refined to some degree. He concludes:
In view of all the above, n’choshet would correspond to nature in its still unrefined state; silver to the purity and goodness that can be acquired by refining; and gold to that pristine, perfect purity and goodness which can withstand any test. N’choshes would represent the ignoble nature; silver, the one who is ready to be ennobled by purification; gold, the original and test-resisting, the most complete purity and goodness.
The Avot instilled the Jewish people with the awareness that the focus of life is ethical and spiritual development. Self-examination, and the personal refinement and moral growth that come in its wake, were represented by the use of gold, silver and brass in the Mishkan. Rav Hirsch reveals to us that when the Torah directed the use of these materials in the Mishkan, we were merely reminded of the Avot and their unique role in establishing Jewish identity, but were actually required to build the ideals by which they lived into the fabric of its building.