הלכה על סנהדרין 165:21

That is that He commanded the priests to wear special garments for glory and adornment, so they can then serve in the Temple. And that is His saying, "And make holy garments for your brother Aharon, for glory and adornment" (Exodus 28:2); "Then bring his sons forward; clothe them with tunics" (Exodus 29:8). And this is the commandment of the priestly garments - eight garments for the high priests and four for an ordinary priest. And anytime the priest serves with less than this number of special garments, or more than them, his service is disqualified and he becomes liable for death at the hands of the Heavens - meaning for the one was lacking clothes and served. And likewise did they count him in the Gemara (Sanhedrin 83b) as one of those liable for death at the hands of the Heavens. And this explanation does not appear in Scripture. But what does appear in Scripture is, "and you shall gird them with sashes [...] and they shall have priesthood" (Exodus 29:9). And the explanation appears - when their garments are upon them, their priesthood is upon them; when their garments are not upon them, their priesthood is not upon them, and they are outsiders (non-priests). Behold it has been made clear to you that an outsider that serves [in the Temple receives] the death penalty. And they said in the Sifra (Sifra, Tzav, Mechilta d'Milium 1:7), "'And he placed the breastplate upon him': This section was learned for its time and for [all the] generations; for the daily service and for the Yom Kippur service. [However] every day he serves in the golden garments; and on Yom Kippur, in the white (linen) garments. And it already appears in the [Sifra], that wearing these garments is a positive commandment. And this is their saying (Sifra, Acharei Mot, Chapter 8:10), "From where [do we know] that Aharon did not wear the garments for his aggrandizement, but only to fulfill the decree of the King? As it is stated, 'and he did as the Lord commanded Moshe' - that is to say, the wearing of the garments." And even though they are the utmost in beauty - given that they are from gold, onyx, jasper and the other precious and beautiful stones - he should not have intention [in wearing them,] for their beauty, but rather only to fulfill the command that God, may He be exalted, commanded Moshe. And that is that he always wear these garments in the Temple. And the regulations of this commandment have already been explained in Zevachim, Yoma and Sukkah. (See Parashat Tetzaveh; Mishneh Torah, Vessels of the Sanctuary and Those who Serve Therein 10.)

To not eat tevel: To not eat tevel - whether an Israelite or a priest - and that is a thing that tithes and priestly tithes have not been taken away from it, as it is stated (Leviticus 22:15), "And they shall not profane the consecrated things of the Children of Israel that they shall raise to the Lord." And the received (traditional) explanation comes about this (Sanhedrin 83a) that the verse is speaking about tevel. And the content of the verse is to say that they should not profane the consecrated things in their still being mixed with the non-sacred. And that is [why] the expression is [in] future tense - meaning to say that it has not yet been raised. And so [too], is it in the Gemara Sanhedrin 83a, "From where [do we know] about the one who eats tevel that he is [punishable by] death? As it is stated, 'And they shall not profane the consecrated things of the Children of Israel that they shall raise to the Lord' - the verse is speaking about those that will be raised in the future; such that we learn [a comparison of] 'profane' [and] 'profane' from priestly tithe," about which it is written (Numbers 18:32), "and the consecrated things of the Children of Israel you shall not profane and not die." And [the latter] is with the death penalty - as we wrote above (Sefer HaChinukh 280), from that which is written (Leviticus 22:9), "and die for it, since they profaned it," and adjacent to it, "And any foreigner shall not eat the holy." And they, may their memory be blessed, also said about this matter in the Gemara Makkot 16b, "Perhaps one is only liable for eating tevel from which no [gifts] were taken at all; but if the great priestly tithe was taken from [the produce], but not the tithe of the tithe, or the first tithe or the second tithe, or even if only the poor tithe [was not separated]; from where [is it derived] that there is a liability in the thing? [Hence] we learn to say, 'You may not eat in your gates' (Deuteronomy 12:17), and later it states, 'and they shall eat within your gates and be satisfied' (Deuteronomy 26:12). Just as there, it is poor tithe, here too, it is poor tithe - and the [Torah] states, 'You may not.'"