Yoma, Chapter Seven, Mishnah One
After having sent the goat away, the Yom Kippur rituals continue with the priest reading various verses from the Torah concerning Yom Kippur and reciting some blessings.
1) The high priest [then] came to read.
2) If he wished to read in linen garments, he reads, and if not he reads in his own white cloak.
3) The synagogue attendant would take a Torah scroll and give it to the head of the synagogue, and the head of the synagogue gives it to deputy high priest, and the deputy high priest gives it to the high priest, and the high priest stands and receives it, and reads, [section] beginning] After the death . . . (Leviticus 16:1-34) and But on the tenth. . . (Leviticus 23:26-32).
4) Then he would roll up the Torah scroll and put it in his bosom and say, More than what I have read out before you is written here. And On the tenth . . . (Numbers 29:7-11) which is in the Book of Numbers he recites by heart.
5) And he recites on it eight benedictions: For the law, For the Temple service, For thanksgiving, For the forgiveness of sins and For the Temple on its own, and For Israel on its own and For Jerusalem on its own, For the priests on their own and For the rest of the prayer.
Section one: The next step was for the high priest to read the portions of the Torah concerning Yom Kippur. This is not mentioned in the biblical description of Yom Kippur. It seems to me that the point of this part of the ritual was to emphasize to both the participants and the observers that everything that the high priest had done was according to the prescriptions of the Torah. It may also have been intended to make a statement about the importance of the Yom Kippur ritual vis a vis Torah. It is as if to say that the rituals significance is in the fact that it is anchored in Torah.
Section two: While reading, the high priest can wear either his special linen clothes (see above 3:6) or he may wear a different cloak. Since the reading is not prescribed by the Torah and is not considered an avodahpart of the days servicehe need not wear the special garments.
Section three: There is a ceremonial passing of the Torah scroll which occurs before the high priest reads it. The first to take it is the synagogue attendant (chazzan). As an aside, this mishnah is an interesting reference to a synagogue that was actually adjacent to the Temple Mount. In 1913 archaeologists found an inscription (see below) on the southern part of the Temple mount which shows that there was a synagogue there while the Temple still stood. The synagogue attendant passes the Torah on to the head of the synagogue (a position referred to in the inscription). The head of the synagogue passes it to the deputy high priest, the second in command, who finally passes it up to the high priest. This procession is clearly meant to pay homage to the high priest. The high priest then reads from the two portions in Leviticus that deal with Yom Kippur.
Section four: The high priest then rolls up the Torah scroll and states to the people that there is more in the Torah about Yom Kippur then that which he has just read. This declaration allows them to know that the passage that he is about to read to them from Numbers is also in the Torah, lest they think he is making it up. He recites the passage from Numbers by heart in order to avoid having to roll from Leviticus until Numbers. Although he did have to roll between the two parts of Leviticus, this was less problematic because the portions are close to one another.
Section five: Finally, he recites eight blessings. The full version of the blessings is not found here; rather the mishnah makes only short references to these blessings. Some of these are familiar because they are still recited today. For the Torah is the blessing recited before reading the Torah today. For the Temple service is part of the Amidah (the 17th blessing). For thanksgiving is also part of the Amidah (the 18th blessing). For forgiveness of sins is similar to that which is also recited in todays Amidah (6th blessing). The other four blessings are unique to the Yom Kippur ritual.
In case you might be interested, the following is a translation of the inscription found at the Temple Mount (I found this on the web):
Theodotus, son of Vettanos, a priest and an archisynagogos, son of an archisynagogos grandson of an archisynagogos, built the synagogue for the reading of Torah and for teaching the commandments; furthermore, the hostel, and the rooms, and the water installation for lodging needy strangers. Its foundation stone was laid by his ancestors, the elders, and Simonides.