“…You shall not offer upon it any other incense, burnt-offering, or flour-offering, and you shall pour no libation upon it…” – Shemot 30:9

The Inner Mizbei’ach, the golden altar which stood in the sanctuary of the Mishkan, was used exclusively for the offering of Ketores, incense. All other Korbanos, the animal and grain offerings, were brought only on the Outer Mizbei’ach that stood in the Mishkan courtyard.

Chassidut explains that the specifics of the service in the physical Mishkan must be equally applied in the spiritual Mishkan that we each must create within ourselves. In the personal spiritual Mishkan, these two altars represent two levels of passion and interest, what Chassidut terms the “outer heart” and the “inner heart.” The “outer heart” refers to interests that are intellectually generated, such that they are inherently limited and contained. The “inner heart,” however, refers to passions that we are drawn to with a profound sense of attachment and inner delight, such as toward causes that directly affect our very survival.

Therein lays the explanation for why no offerings other than the Ketores could be brought on the Inner Mizbei’ach. The animal and grain Korbanos represent a Jew’s responsibilities toward the world in which he lives, to uplift it from its mundane existence and infuse it with G-dly meaning. Like the blood, fats and grains that were offered up to G-d on the altar, the Jew must elevate all his mundane activities by directing them toward a G-dly objective and purpose. Nevertheless, the Korbanos were brought on the Outer Mizbei’ach to show that one’s involvement in the material world, even if directed toward a higher goal, must never become his inner passion and zeal.

Ketoret, conversely, represent the Jew’s efforts within himself to develop a deeper and more meaningful relationship with G-d. The word Ketoret, קטורת, is thus related to the Aramaic word קטר, a knot, referring to the inner bond with G-d that a Jew cultivates through the study of G-d’s Torah and the observance of His commands. Only these exclusively holy endeavors may be offered on one’s Inner Mizbei’ach, i.e., pursued with inner devotion, passion and delight.

—Likkutei Sichos vol. 6, pp. 185-187