Acharei Mot-Kedoshim(Leviticus 16-20)
The Torah portion begins with a description of the service performed on Yom Kippur in the Mishkan and later in the Beis HaMikdash.
God said to Moshe, "Speak to Aharon, your brother, that he should not come any time to the holy place, to the house of the curtain, toward the face of the covering which is upon the Ark, so that he should not die, for in a cloud I will appear over the covering. With this shall Aharon come to the holy place..." (Vayikra 16:2-3)
The verses continue by detailing all of the procedures that the kohen gadol must execute on that great day. The surprising thing is the verses give us no indication as to which day they are referring! Rashi tells us:
With this - even this cannot be done on any day except for Yom Kippur, as is explicit at the end of the parshah: In the seventh month, on the tenth day... (Vayikra 16:29). (Rashi loc. cit.)
All of this seems out of sequence. We would have expected the Torah to tell us at the start of the parsha that the day on which Aharon could come to the holy place was Yom Kippur, rather than leave us in suspense until the end of the parshah. The Zohar HaKadosh actually asks this question directly:
The verse says, Do not come just at any time to the holy place. Since it tells him not to come at any time, why is it not written at which time he should come? (Zohar HaKadosh 2:28b)
zayin, alef, tav. The zayin at the start of the word (which has the numerical value of seven) hints at the seven days of Creation, which point to the natural order. The remaining two letters, alef and tav, are, respectively, the first and last letters of the alef-beis. This hints at the letters of the Torah, which are imbued with supernatural powers, pointing to the supernatural order.
There are entirely natural events which happen in the world directed by the forces of nature - the laws of physics, chemistry, thermodynamics, etc. There are some completely supernatural events, such as the Splitting of the Sea, the existence of the pillars of fire and the cloud which accompanied klal Yisrael in the wilderness, and the daily arrival of the manna. However, there is a third category of occurrences, in which one can see manifestations of both natural and supernatural forces. The subject of the occurrence does not change miraculously (like at the Splitting of the Sea), but something about it is out of the ordinary. Let us give some examples:
The place of the Ark [in the Beis HaMikdash] was not counted in the measurement. (Megillah 10b)
This means that although the Ark was physically in the Holy of Holies, it miraculously occupied no space, for the floor area filled all of the dimensions without the Ark, which was nevertheless included. With respect to Eretz Yisrael, when people live in it, it expands [to accommodate them], and when people do not live in it, it contracts. (Gittin 56a)
In the Beis HaMikdash ... the people stood crowded together; nevertheless, they prostrated with plenty of space ... (Mishnah, Avos 5:7)
These miracles all displayed the hand of God, but in a more subtle way than the open miracles of the Splitting of the Sea and the like. The Ark, Eretz Yisrael, and the courtyard in the Beis HaMikdash all appeared completely normal. But none of them functioned within the normal space-frame. This sort of miracle is expressed by the word zos, which is a conjunction of the natural order and the supernatural order: zayin plus alef and tav.
beis din. When the Beis HaMikdash stood, Rosh Chodesh was declared according to testimony from witnesses who had seen the new moon. This determined the day on which yom tov would fall. Additionally, food preparation is permitted on Yom Tov. All of this points to a different style of day, one in which the human element is much more evident. Yom tov focuses more on the physical world than does Shabbos and on sanctifying that world; it primarily expresses the natural dimension of existence.
Yom Kippur is somewhere in between the two. It is a yom tov, and, as such, the day on which it falls is determined by beis din according to the evidence of those who have seen the new moon. However, Yom Kippur has all of the Shabbos restrictions. So Yom Kippur is a combination of the natural concept expressed by yom tov and the supernatural concept expressed by Shabbos. It is indeed a zos type of day.
Regarding the human soul, we may suggest that the kohen gadol expresses this combination. On one hand, he is a normal human, like any other. On the other, he assumes superhuman qualities when performing his Divine service on Yom Kippur:
No man may be in the Ohel Mo'ed when he goes in to atone in the holy place, until he exits... (Vayikra 16:17)
No man may be in the Ohel Mo'ed - was not the kohen gadol a man?...Rather, when the Divine spirit rested on him, his face gleamed like a firebrand. [He was like an angel.] (Vayikra Rabbah 21:12)
At the zenith of his yearly service, the kohen gadol reached such a great level of Divine communion that he was no longer considered a human being; temporarily he resembled an angel. Thus even when he himself was inside the Holy of Holies, it was nevertheless as if no man was there! We thus see the zos concept expressed within the kohen gadol, for he was both a man (the natural element) and an angel (the supernatural element).
It is not surprising that these three manifestations of zos, in space, time, and the human soul, all coincide. For as we have seen, the kohen gadol goes into the Holy of Holies on Yom Kippur. All of this is hinted at by the magic word zos.
This should help us to understand the order of the verses and why it is that we don't discover that the whole parshah refers to Yom Kippur until after the laws have been recorded. We learned that Aharon should not "come just at any time to the holy place." "Any time" refers to the natural order, an ordinary day in the year, on which the kohen gadol may not enter the holy place. But the following verse tells us when he may: when zos is applicable in all of its facets. Thus on Yom Kippur, the kohen gadol may enter the Holy of Holies. So the Torah actually does tell us when the offerings that are described will apply - by preceding the whole parshah with zos, we know that the special day to which it refers is Yom Kippur.