Man’s quest to serve his Creator is perpetual and all-consuming, and can be pursued by all people, at all times, and in all places. There was one event, however, that represented the apogee in the human effort to come close to G-d—an event that brought together the holiest day of the year, the holiest human being on earth, the holiest place in the universe and the holiest of deeds. On Yom Kippur the Kohen Gadol (“High Priest”) would enter into the “Holy of Holies” (the innermost chamber of the Holy Temple in Jerusalem) to offer ketoret to G-d.
The offering of the ketoret was the most prestigious and sacred of the Temple services. The ketoret was a special blend of eleven herbs and balms whose precise ingredients and manner of preparation were commanded by G-d to Moses. Twice a day, the ketoret was burned on the “golden altar” that stood in the Temple. On Yom Kippur, in addition to the regular ketoret offerings, the Kohen Gadol would enter the Holy of Holies with a pan of smoldering coals in his right hand and a ladle filled with ketoret in his left; there he scooped the ketoret into his hands, placed it over the coals, waited for the chamber to fill with the fragrant smoke of the burning incense, and swiftly backed out of the room. The moment marked the climax of the Yom Kippur service in the Temple.
Maimonides describes the function of the ketoret as the vanquishing of the unpleasant odors that might otherwise have pervaded the Holy Temple.
“Since many animals were slaughtered in the sacred place each day, their flesh butchered and burnt and their intestines cleaned, its smell would doubtless have been like the smell of a slaughterhouse… Therefore G-d commanded that the ketoret be burned twice a day, each morning and afternoon, to lend a pleasing fragrance to [the Holy Temple] and to the garments of those who served in it.” 
But Maimonides’ words carry a significance that extends beyond their superficial sense. In the words of Rabbeinu Bechayei:
“G-d forbid that the great principle and mystery of the ketoret should be reduced to this mundane purpose.” 
Chassidic teaching explains that the animal sacrifices offered in the Holy Temple represent the person’s offering of his own “animal soul” to G-d—the subjugation of his natural instincts and desires to the divine will. This is the deeper significance of the “foul odor” emitted by the sacrifices which the ketoret came to dispel: the “animal soul” of man, which is the basic drive, common to every livining creature, for self-preservation and self-enhancement, possesses many positive traits which might readily be directed toward gainful and holy ends; but it is also the source of many negative and destructive traits. When a person brings his animal self to the Temple of G-d and offers what is best and finest in it upon the altar, there is still the “foul odor”—the selfishness, the brutality and the materiality of the animal in man—to contend with. Hence the ketoret, which possessed the unique capability to sublimate the evil odor of the animal soul within its heavenly fragrance.
Essence and Utility
This, however, still does not define the essence of the ketoret. For if the more external parts of the Temple might be susceptible to the foul odor emitted by the “animal souls” offered there, the Holy of Holies was a sanctum of unadulterated holiness and perfection. If the “garments” (i.e., character and behavior) of the ordinary Kohen might be affected by the negative smell of the “slaughtered beasts” that he handled, this is certainly not the case with the Kohen Gadol, “the greatest of his brethren” in the fraternity of divine service. If every day of the year the scent of evil hovers at the periphery of even the most positive endeavor, Yom Kippur is a day in which:
“There is no license for the forces of evil to inculpate.” 
So if the ketoret was offered by the Kohen Gadol in the Holy of Holies on Yom Kippur, its ultimate function cannot be the sublimation of evil.
The sublimation of evil is something that only the ketoret can achieve, but this is not what defines its essence. The essence of the ketoret is a pristine yearning of the soul of man to come close to G-d, a yearning that emanates from the innermost sanctum of the soul and is thus free of all constraint and restraints, of all that inhibits and limits us when we relate to something with the more external elements of our being. Its purity and perfection is what gives the ketoret the power to sweeten the foulest of odors, but dealing with evil is not what it is all about. On the contrary, its highest expression is in the utterly evil-free environments of Yom Kippur and the Holy of Holies.
Bringing the Past In Line
Today, the Holy Temple no longer stands in Jerusalem, and the Kohen Gadol enters the Holy of Holies only in our recitation of the account of the Yom Kippur service in the prayers of the Holy Day and in our vision of a future Yom Kippur in the rebuilt Temple. But the ketoret remains a basic component of our service of G-d in general, and of our observance of Yom Kippur in particular. We are speaking, of course, of the spiritual ketoret, which exists within the human soul as the potential for teshuvah.
Like the incense that burned in the Holy Temple, the manifest function of teshuvah is to deal with negative and undesirable things. On the day-to-day, practical level, teshuvah is “repentance”— a response to wrongdoing, a healing potion for the ills of the soul. But teshuvah is also the dominant quality of Yom Kippur, the holiest day of the year. Obviously, there is more to teshuvah than the neutralization of sin.
The word teshuvah means “return”: return to pristine beginnings, return to the intrinsic perfection of the soul. For the essence of the soul of man, which is “a spark of G-dliness,” is immune to corruption. The inner self of man remains uninvolved in the follies of the ego, untouched by the outer self’s enmeshment in the material and the mundane. Teshuvah is the return to one’s true self, the cutting through of all those outer layers of misguided actions and distorted priorities to awaken one’s true will and desire.
This explains how teshuvah achieves atonement for past sins. Teshuvah enables the sinner to touch base with his own inherent goodness, with that part of himself which never sinned in the first place. In a sense, he has now acquired a new self, one with an unblemished past; but this “new self” is really his own true self come to light, while his previous, corrupted “self” was but an external distortion of his true being.
Only teshuvah has such power over the past; only teshuvah can “undo” a negative deed. But this is only one of the “uses” of the power of return. Teshuvah is not only for sinners, but also for the holiest person in the holiest time and the holiest place. For even the perfectly righteous individual needs to be liberated from the constraints of the past.
Even the perfectly righteous individual is limited—limited because of knowledge not yet acquired, insights still ungained, feelings yet to be developed, attainments still unachieved; in a word, limited by time itself and the tyranny of its “one way only” traffic law. As we advance through life, we conquer these limits, gaining wisdom and experience and refining and perfecting our self and character. But is our ability to grow and achieve limited to the future only? Is the past a closed frontier?
But one who adopts the inward-seeking approach of teshuvah to everything he does, never leaves an imperfect past behind at the waysides of his life. When he learns something new, he uncovers the deeper dimension of his own self which was always aware of this truth; when he refines a new facet of his personality, he brings to light the timeless perfection of his soul. Never satisfied in merely moving forward, his search for his own true self remakes the past as well.
Based on the Rebbe’s talks, Simchat Torah 5727 (1966); Sivan 14, 5746 (June 21, 1986); and on other occasions
Adapted from the teachings of the Rebbe by Yanki Tauber
. Exodus 30:34-38; see Talmud, Keritot 6a and Jerusalem Talmud, Yoma 4:5.
. Exodus, ibid., vs. 8-9.
. Leviticus 16:12-13; Talmud, Yoma 5:1 (mishnah).
. Guide for the Perplexed, part III, ch. 45.
. Rabbeinu Bechayei on Torah, Exodus 30:1.
. As Rabbi Schneur Zalman of Liadi elaborates in his Tanya, every person possesses two souls: an “animal soul” that is the essence of his physical self, and a “G-dly soul” that embodies his drive for self-transcendence and union with G-d.
 . See Tanya, chs. 4 and 6.
 . Leviticus 21:10.
. Talmud, Yoma 20a.
 . Cf. Zohar, part III, 288a.
 . Likkutei Sichot, vol. XIV, pp. 129-131; Hitvaaduyot 5746, vol. III, pp. 583-584; et al.