From the Chassidic Masters

In his Likkutei Torah Rabbi Schneur Zalman of Liadi explains that the altar represents the heart. Corresponding to the two altars of the Sanctuary, the outer and the inner, are the outer and inner levels of the heart, its surface personality and its essential core. And the altar on which the "continual fire" (aish tamid) was to be set was the outer one

Spiritual gluttony is no less selfish than the physical sort, and one who focuses solely on self-realization and self-fulfillment -- be it in the most positive and lofty sense -- is turning his Holy Temple inside out