The artisans then fashioned the Inner Altar and the Outer Altar. These were followed by the Laver and the pillars of the Courtyard.
Blending Assertiveness with Humility
נְבוּב לֻחֹת עָשָׂה אֹתוֹ: (שמות לח:ז)
[As instructed, the artisans made the Outer, copper Altar] as a hollow structure. Exodus 38:7

The Outer Altar is where the process of refining our animal natures took place. The material and form of the Outer Altar allude to the two opposite attitudes we need to cultivate in order to accomplish this:

On the one hand, we must be resolute in our dedication to spiritual advancement. The Jews are called “a stiff-necked people”; this can be a positive quality when it is expressed as determination and obstinacy in realizing spiritual goals. This quality is alluded to by the fact that the Altar was made of copper, since the Hebrew word for “copper” (nechoshet) is related to the Hebrew word for “brazen (nechush) stubbornness.”

On the other hand, the hollow Altar was filled with earth. Similarly, while we must be externally stubborn, internally we must be humble as earth. As we say in our prayers, “and may my soul be as dust to all.”1