The Shabbos between Rosh HaShanah and Yom Kippur is often called Shabbos Teshuvah, the “Shabbos of Repentance,” since it is the Shabbos that falls within Aseres Yemei Teshuvah, the Ten Days of Repentance, that begin with Rosh HaShanah and conclude with Yom Kippur.

Since all ten days share the same name, it follows that they all constitute a single entity whose beginning is Rosh HaShanah and whose conclusion is Yom Kippur. Clearly, then, the preparation for Yom Kippur, the culmination of the Ten Days of Repentance, commences on Rosh HaShanah, the beginning of the Ten Days of Repentance.

The main commandment of Rosh HaShanah is to sound the shofar. The unique service on Yom Kippur is that of the Kohen Gadol, the High Priest; during the rest of the year the service in the Holy Temple could be conducted by other priests, but on Yom Kippur the entire service had to be performed by the Kohen Gadol.

Wherein lies the connection between Rosh HaShanah, the beginning of the Ten Days of Repentance, and its conclusion on Yom Kippur? Seemingly, the service of sounding the shofar on Rosh HaShanah and the service of the Kohen Gadol on Yom Kippur are entirely different.

A deeper understanding of the service of the Kohen Gadol on Yom Kippur will help us comprehend the connection between the two:

There were two aspects to the Kohen Gadol’s service on Yom Kippur: the service that he performed in garments of gold outside the Holy of Holies; and the main aspect of his service, performed within the Holy of Holies while wearing simple linen garments.

Whenever the priests would perform the service in the Temple, they would wear garments that served both to “honor and adorn.”1 The reason for wearing garments that “honor and adorn” is that one should employ that which is most beautiful in the service of G‑d. Truly, this was also why the Kohen Gadol performed the service outside the Holy of Holies in garments of gold, since these are most impressive.

This being the case, why was it that within the Holy of Holies — a place where only the Kohen Gadol was permitted, and then only once a year on Yom Kippur, at which time he achieved atonement for the entire Jewish people — did he perform his service in simple linen garments?

The reason for this is as follows. Although the destruction of the Temple led to the cessation of the Kohen Gadol’s service there on Yom Kippur, the spiritual Temple found within each and every Jewish soul was never destroyed.

Within this spiritual Temple there also exist different degrees of service according to the specific time of year. With the arrival of Yom Kippur, each Jew — serving as the Kohen Gadol of his own personal Temple — is to perform his own internal service of the Kohen Gadol.

This service is composed of the individual serving outside the Holy of Holies in garments of gold, and serving within the Holy of Holies of his soul in linen.

This means that when serving outside the Holy of Holies, i.e., when one is not serving with the innermost core of his spiritual being, one should adorn his service so that those physical things that are most dear to the person (“gold”) are used for spiritual (“Temple”) purposes.

However, when it comes to the “Yom Kippur” and the “Holy of Holies” within a Jew’s soul, the quintessence of the soul, physical adornment is of no benefit, for what is desired is simplicity — a service of simple faith and self-sacrifice wherein all Jews can serve equally.

This theme of simplicity is also found with regard to the sounding of the shofar, a simple animal horn that does not emit melodious sounds but “merely” produces simple notes.

On Rosh HaShanah a Jew comes before G‑d with a simple heart-rending cry, the plaintive sound of the shofar that comes from the depth of his heart, beseeching G‑d for a good and sweet year.

Through his service during the Ten Days of Repentance, culminating in the essential purity and simplicity of his soul on Yom Kippur, the Jew merits to have his request granted: he is “sealed” for a good and sweet year.

Based on Likkutei Sichos, Vol. II, pp. 411-413.