According to Lev 16:1, the Yom Kippur ceremony was initiated after Aaron’s sons erred in their priestly duties in the Temple’s Holy of Holies. They had offered incense with a strange fire (inappropriately kindled), and were immediately burned to death in the Temple by a flame which erupted from Jehovah (Le 10:1). After this incident, Jehovah forbids all priests from entering into the Holy of Holies, except for the high priest one day each year on Yom Kippur. Even then, the high priest could only enter after going through the elaborate series of sacrifices and rites specified in Lev 16. Edersheim describes this in great detail from rabbinic sources. The ceremony began with the high priest entering the court of the priests with a young bullock and two goats. The bullock would be a sin offering for himself, so that he might complete his duties. One of the goats would be selected to be an atonement for all the people, including the priest himself. The priest confessed his and Israel’s sins over the head of the bullock, which stood between the temple-porch (beyond which was the Holy of Holies) and the altar. He then moved to the eastern part of the Court of Priests, which was close to the worshippers. There stood an urn, called Calpi, in which were two lots of the same shape, size, and material. In the second Temple, they were of gold. One bore the inscription l’Yahweh (“for Jehovah”) and the other l’Azazel (“for Azazel”). The two goats stood north of the altar facing the sanctuary (westwards), with their backs to the people. The high priest faced the people and stood between the goats as he shook the urn, thrust his two hands into it and simultaneously withdrew the two lots, one in each hand. He then placed each hand’s lot upon the goat on that hand’s side. It was deemed good augury if the right-hand lot had fallen “for Jehovah”, which was the goat closest to the altar. The high priest immediately tied a scarlet cloth to the horns of the goat for Azazel so that it would not be confused with the one whose lot was to Jehovah. The goat for Azazel was then turned round towards the people, and waited there facing the people as the next part of the ceremony unraveled.
The high priest returned once more towards the sanctuary, and there he slew the young bullock and caught its blood in a vessel. He handed this vessel to an attendant who kept this blood stirring so it would not coagulate. The priest then carefully entered the Holy of Holies, bearing a censer and incense. Tradition has it a rope was tied around one of his ankles, so if he was stricken down dead by Jehovah, his body could be retrieved without subjecting anyone else to danger. Once inside the he emptied the incense on the coals of the censer, and waited until the smoke had filled the Holy of Holies. He then exited, took the blood of the bullock, returned, and sprinkled the blood within the Holy of Holies. He exited again, and deposited the vessel with the blood upon a golden stand before the veil of the Holy of Holies. The high priest then killed the goat set apart for Jehovah and entered the Holy of Holies a third time. He sprinkled the goat’s blood as before, and upon exiting he set the vessel with the goat’s blood upon a second golden stand. He then took blood from the goat and the bullock’s vessel, and sprinkled the veil of the Holy of Holies. He then did a very profound act. He poured the bullock’s blood into the bowl which contained that of the goat, and mixed the two thoroughly together. He then sprinkled the altar of incense with this mixture. This mixing of blood showed that the two sacrifices had become one in their expiatory power.
That which was left of the blood the high priest poured out on the west side of the base of the altar of burnt offering. At this point, the high priest had cleansed the sanctuary in all its parts from the defilement of the priesthood and the worshippers. The Holy of Holies, its veil, the golden altar of incense in the Holy Place, and the altar of burnt offering in the court of the priest were now clean alike. Both the priesthood and the sanctuary were now atoned for in their relationship to Jehovah. Yet the ceremony was not over. The goat to Azazel, which had stood confronting the people with its scarlet scarf, remained.
All the peoples own personal guilt and sins were now to be removed from them, and placed upon the goat. The high priest laid both his hands on the goat’s head and pleaded:
Ah, Jehovah! they have committed iniquity; they have transgressed; they have sinned — Thy people, the house of Israel. Oh, then, Jehovah! cover over (i.e. atone for), their iniquities, their transgressions, and their sins, which they have wickedly committed, transgressed, and sinned before Thee. As it is written in the law of Moses, Thy servant, saying: “For on that day shall it be covered over (i.e. atoned) for you, to make you clean from all your sins before Jehovah you shall be cleansed.”
The priests then removed half the scarlet wool cloth from the goat’s horns and affixed it to the Sanctuary door. They then led the sin-burdened goat out through Solomon’s Porch and then through the eastern gate. Here an arched bridge spanned the intervening valley, and they brought the goat over this to the Mount of Olives, where a ready man, specially appointed for the purpose, took charge of the goat. After a substantial journey, passing through several stations where others would accompany him for a while, he finally reached a rocky cliff area at the edge of the wilderness known alternatively as Dudael, Beth Hadudo, or simply Azazel. He then pushed the animal backwards over the rock ledge. The goat plummeted below, and before reaching the halfway point its limbs would be ripped off. In the final years of the Temple (after 30 CE), the slaying of the goat was immediately telegraphed, by the waving of flags from station to station, so that a few minutes after its occurrence it was known in the Temple. However, tradition has it that in years when the sacrifice was accepted, this was not done as the people immediately knew the result because the half of the scarlet wool cloth affixed to the Sanctuary door had turned white the moment the goat had hit the bottom of the cliff.
 Talmud Yomah 6 state that the rabbis taught that formerly the tongue of crimson wool used to be tied to the door of the porch, on the outside so that all should see. When it became white, the people rejoiced; when not, all became out of spirits and ashamed. Therefore it has been reformed that it should be tied to the door of the porch inside. However, the people used to take a look at it even then. It was then reformed that half should be tied to the rock at the cliff in the wilderness, another half to the horns. These later reforms may have come late, after the miracle of scarlet wool cloth stopped in 30 CE, as the priests did not wish to distress the people.