The altar that stood in the courtyard of the Mishkan was coated with a layer of copper. Rashi explains that copper is a metaphor for brazenness (see Yeshayahu 48:4), and the Mizbe’ach atoned for Bnei Yisrael’s insolent behavior.
The copper coating also represented a positive form of brazenness and chutzpah, which is demanded of Bnei Yisrael: a Jew must be bold and unashamed about his Judaism, defiant and unfazed by anyone who might mock his worship of G‑d.
Beneath its tough exterior, however, the Mizbe’ach was hollow. Wherever Bnei Yisrael erected the Mishkan, they filled the Mizbe’ach with earth, to symbolize that even while approaching a challenge with toughness and chutzpah, deep down we must always feel humble, like insignificant, trampled earth.
These two aspects of the Mizbe’ach, its copper coating and its hollow inside filled with earth, thus represent two opposite yet vital traits that are always required of a Jew.
—Reshimos, no. 108
