And he shall take a coal pan full of coals of fire from off the altar from before the Lord, and his hands full of sweet incense beaten small and bring it within the veil. And he shall put the incense upon the fire before the Lord, and the incense cloud shall cover the Ark cover that is upon the Testimony, and he will not die. And he shall take from the blood of the bull, and he shall sprinkle it with his finger upon the Ark cover to the east, and before the Ark cover he shall sprinkle seven times from the blood with his finger. And he shall slaughter the goat of the sin-offering that is for the people, and bring its blood within the veil, and he shall do with its blood as he did with the blood of the bull, and sprinkle it upon the Ark cover and before the Ark cover. And he shall make atonement for the sacred place because of the impurities of the children of Israel, and because of their transgressions, even all their sins; and so shall he do for the Tent of Meeting that dwells with them in the midst of their impurity. And there shall be no man in the Tent of Meeting when he goes in to make atonement in the sacred place, until he comes out and has atoned for himself and for his household and for the assembly of Israel. And he shall go out to the altar that is before the Lord, and make atonement for it; and he shall take of the blood of the bull and of the blood of the goat, and put it on the corners of the altar round about. And he shall sprinkle of the blood upon it with his finger seven times, and cleanse it and sanctify it from the impurities of the children of Israel. (Leviticus 16:12–19)

And you shall make an altar to burn incense, of acacia wood you shall make it. A cubit shall be its length and a cubit its breadth, it shall be square, and two cubits shall be its height, and its corners shall be one piece with it...And Aaron shall make atonement upon its corners once a year; with the blood of the sin-offering of atonement once a year he shall make atonement for it throughout your generations; it is most sacred to the Lord. (Exodus 30:1–2; 10)

This chapter continues to describe, following the order of the verses and the service of the day, the rites of the High Priest. It focuses mainly on the services that are at the heart of Yom Kippur, namely the rites performed within the inner sanctum, the Holy of Holies. The High Priest is permitted to enter this chamber only on Yom Kippur, and solely for the purpose of these services.

The first stage of these rites is the scooping of a handful of incense and its presentation. The practical performance of this action entails numerous difficulties with regard to the scooping itself, the amount of incense required, and the manner in which it is burned inside the Holy of Holies. Furthermore, the Second Temple differed from both the First Temple and the Tabernacle in the wilderness in that it lacked the Ark of the Covenant and possessed certain structural differences. Therefore, the precise route of the High Priest's entrance into the Holy of Holies and his service inside the inner sanctum require elucidation. Likewise, the commandment that the High Priest be alone in the Sanctuary while performing the service in the Holy of Holies raises various issues, particularly with regard to the exact delineation of the Sanctuary area.

After concluding the service in the Holy of Holies, the High Priest performed additional rites in the Sanctuary, i.e., the sprinkling of the blood on the curtain and the golden altar, also called the incense altar. These rites too are performed almost exclusively on Yom Kippur. The order of the sprinklings on the curtain and the altar must be clarified in detail, from the spot where they are performed to the disposal of the remainder of the blood.

The Yom Kippur service differs from the regular Temple service in two ways: On the one hand, it is especially important that the Yom Kippur service is performed in the exact order prescribed by the Torah. If the High Priest deviates from this order, the service is invalid. On the other hand, generally speaking, the High Priest does not complete all the rites of one offering from start to finish without interruption; rather, he is constantly moving from one rite to another, and from one offering to another. Consequently, it is easy to fall prey to error in one of the rites, particularly with respect to their order. This chapter addresses those cases where the High Priest made a mistake in this regard, and discusses which errors disqualify the service and which do not. Similarly, if a certain rite was disqualified or interrupted, the Gemara inquires as to at what point in the service the High Priest is obligated to start over.

These and related issues form the content of Chapter Five.