The name Yom Kippur means "Day of Atonement"; it is "the
culmination of forgiveness and pardon for Israel." 
The Hebrew term for "atonement" - kapparah, implies not only that
the sinner will not be punished for his transgressions, but also
that the spiritual blemishes caused by sin will be washed away
from his soul.
When a person turns to G-d in sincere teshuvah, the process
of change can purge, and even transform, the negative spiritual
influences generated by sin. 
It is, however, difficult to understand how can this be
accomplished by the arrival of Yom Kippur on the calendar.
How can Yom Kippur itself bring about such a dramatic change
in a person's being?
The Essence of the Day Atones
This question lies at the heart of a difference of opinion among
our Sages. 
Rabbi Yehudah HaNasi maintains that atonement is granted on Yom
Kippur whether or not a sinner repents, because "the essence of
the day (itzumo shel yom mechaper) atones." 
The majority of the Sages differ with this view, maintaining
that Yom Kippur atones only for those who repent. 
However, even those Sages acknowledge the power of "the essence
of the day," in their statement that on Yom Kippur we can atone
for sins which cannot be completely atoned for on other days. 
The difference between the Sages and Rabbi Yehudah HaNasi, then,
is that the Sages maintain that "the essence of the day" can only
affect an individual who through teshuvah has opened his heart to
its influence. Rabbi Yehudah HaNasi, by contrast, maintains that
the influence of "the essence of the day" is so powerful that it
atones even without teshuvah.
In order to understand this difference of opinion, we must
analyze the nature of "the essence of the day" and how can
it bring about an internal change within a person.
Three Levels of Connection
We relate with G-d at three levels. 
The first level of connection is based on a person's Torah
observance: his intellect grapples with Torah study, his emotions
find expression in the love and fear of G-d, and his potential
for activity is actualized in the performance of mitzvos.
The second level of connection is deeper than that which can be
achieved through thought or word or deed. This bond surfaces even
when the Torah-based connection to G-d has been severed. At this
level, though sin may separate a person from G-d, he will be
inspired to turn to Him through the potential for teshuvah. 
Finally, there is a level of connection to G-d which stems from
the fact that the essence of the Jewish soul is one with the
essence of G-d.
This bond is constant.
At all times, our essence "cleaves to You." 
This bond is not the result of our efforts, and consequently,
neither our thoughts nor our words nor our deeds can weaken it.
The connection to G-d established through Torah observance is
limited by the extent of each individual's religious commitment
and actual observance.
Furthermore, since this connection is humanly generated, it is
limited, no matter how inspired and complete our observance is.
Even teshuvah - though it results in a deeper connection than
that effected by observance - is limited, because it too requires
human input: our yearning not to be separated from G-d.
The essential bond we share with G-d, however, does not depend on
us at all, coming about instead, because our souls are "an actual
part of G-d from above."  At this level of essential
connection, there is no existence outside G-dliness, no
possibility of separation from G-d, no possibility that the
soul be affected by sin.
The very revelation of this level of connection removes the
blemishes which sin causes.
This kind of cleansing is a natural process, for the revelation
of one's inner bond renews our connection with G-d at all levels.
When, by contrast, one atones for sin through teshuvah, the
deeper connection he establishes breaks through the barriers
he has created by his past conduct. Revealing one's innate inner
bond with G-d is even more powerful: it leaves no possibility of
This is the meaning of saying that "the essence of the day
On Yom Kippur, one's essential bond with G-d is revealed, and
in the process, every element of our spiritual potential is
Locked In, Alone With G-d
The revelation of this essential bond on Yom Kippur is reflected
in the High Priest's entry into the Holy of Holies, during which
he came into direct contact with the Divine Presence. No human
or spiritual being  was permitted to intrude upon his
connection with G-d.
This same degree of connection can be achieved by each of us
through our divine service on Yom Kippur, and in particular,
during the concluding Neilah service.
Neilah means "closing" or "locking".
At this time, every individual Jew is locked in, alone with G-d.
At this time, the essence of his soul, the level that is one with
the essence of G-d, is revealed.
Neilah is the fifth prayer service of Yom Kippur.
Our Sages explain  that there are five levels within the
The fifth and deepest is called yechidah, from the word yachid
which means "singular oneness."
This is the point in the soul that is united in singular oneness
with G-d; this is the level that surfaces during Neilah. 
The level of soul experienced during Neilah foreshadows the Era
of the Redemption, for Mashiach represents the yechidah of all
existence  and will reveal this unique connection in every
aspect of our being.
May this take place in the immediate future.
- Neilah liturgy; Rambam, Mishneh Torah, Hilchos Teshuvah 2:7.
- See the previous essays entitled "Teshuvah - Return, not
Repentance" and "Transforming Evil."
- Shavuos 13a.
- Toras Kohanim, commenting on Vayikra 16:30.
- This opinion is accepted as halachah (Rambam, loc. cit.
1:3, Hilchos Shegagos 3:10; Shulchan Aruch HaRav 607:16).
- Yoma 86a; Rambam, Hilchos Teshuvah 1:3-4. Significantly,
though the Rambam follows the opinion of the Sages, in
the above halachos he quotes the expression, "the essence
of the day atones."
- See the above essay entitled "At One with the King."
- Similarly, this inner potential inspires a person who has
not sinned to achieve a more powerful relationship with G-d.
- The Hoshanos prayers of the third day of Sukkos.
- Iyov 31:2, as paraphrased in Tanya, ch. 2.
- As explained in Note 8 to the above essay entitled "At
One with the King," both Rosh HaShanah and Yom Kippur
express an essential level of G-dliness that transcends
their more general function as "days of teshuvah."
- Jerusalem Talmud, Yoma 1:5.
- Bereishis Rabbah 14:9; Etz Chayim, Shaar 42, chs. 1-2. On
the Essence of the Teachings of Chassidus (Kehot, N.Y.,
5738) explains these five levels at length.
- Likkutei Torah, Parshas Pinchas, p. 86b.
- See the gloss of the Ramaz to Zohar II, 40b. See also On
the Essence of the Teachings of Chassidus.