vice is invalid); according to the other opinion, this is not obligatory. But how is it known that in the second case this is not obligatory? Because it is written in the Mishna: "A substitute is prepared," and not "removed." What is the reason of him who says that all which is written is obligatory? Said R. Itz'hak bar Bisna: It is written [Ex. xxix. 35]: "And thou shalt do unto Aaron and to his sons, thus." Thus signifies that it is obligatory. This would be right in regard to all the things written in the chapter about the days of consecration; but whence is it known that other things not written in this chapter are also obligatory (e.g., the breastplate and Ephod, not mentioned in that chapter, yet known to be obligatory)? Said R. Na’hman b. Itz’hak: We infer it from an analogy of expression; in that chapter the "door of the tabernacle of the congregation" is mentioned [Lev. viii. 4], and in the chapter about the breastplate, etc. [Ex. xxix. 4] the same expression recurs. (As in the case of practice it is obligatory, so in the case of the commandment.) R. Mesharshia says: It is inferred from "keep the charge of the Lord" [Lev. viii. 35] (an analogy of expression is not necessary, it is plainly said "keep," hence it is obligatory). R. Ashi says, from "for so I have been commanded" [ibid.]; hence it is obligatory.
How did Moses attire Aaron and his sons on the days of consecration? [That is, to understand the verses of the Bible; we wish to know it, although it does not concern us.] The sons of R. Hiya and R. Johanan differ. One party says he attired Aaron first, and the sons next; and the other, Aaron and his sons at the same time. Said Abayi: About the coats and the mitres they do not differ—namely, that Aaron was attired in them first, and the sons later; for both in speaking of the commandments and the practice Aaron is mentioned first [Ex. xxix. 56; Lev. viii. 7]. What they differ about is the girdle. The party who says, "Aaron, and his sons later," does so because it is written, "and girded him with the girdle" [Lev. viii. 7], and later, "girded them with girdles" [ibid. 13]. The party who says they were attired at the same time, do so because it is written, "Thou shalt gird them with girdles, Aaron and his children" [Ex. xxix. 9]. But how can it be said that he attired them at the same time (it is written plainly that first he attired Aaron, and then his sons)? There is a difference between a girdle of the high-priest and that of an ordinary priest. That means, when it is written he girdled Aaron first, it is meant,
