Or HaChaim on Leviticus 16:4/אור החיים על ויקרא ט״ז:ד׳

1 כתנת בד קודש ילבש, "He shall put on the holy linen tunic, etc." The reason the Torah used the word קרש, holy, in connection with the linen tunic and was not content to include it in the subsequently mentioned בגדי קודש, sacred garments, may be that the Torah was afraid that we would reason that G'd had only ordered three garments to be paid for from the treasury of the Temple seeing they are not garments an ordinary person has to wear anyway. Inasmuch as every person has to wear a tunic, it could have been reasoned that Aaron had to pay out of his own funds for that tunic. The Torah therefore added the word קדש, sacred, to teach that this tunic too was paid for by funds from the Temple treasury. The Torah added the words בגדי קודש הם, so that we should not think that only the tunic was to be paid for by the Temple treasury. The Torah wanted to make plain that the same rule applied to all four garments.

2Furthermore, the Torah may have intended to inform us that the material the tunic was made from was paid for by the Temple treasury. The same applied to the other three garments mentioned here. The Torah wanted to make this plain already when mentioning the first garment. The meaning of the words בגדי קודש הם, may be that the cost of constructing the garments, not only their materials, should be defrayed by the Temple treasury.

3The Torah may also have intended to convey that these garments are of holy character by writing the words בגדי קודש הם, One should not think that it is demeaning that the very servant of G'd who had been equipped with eight garments described in Exodus 28,2-5 as לכבוד ולתפארת, "for glory and splendour," should now wear only inferior garments when performing the service inside the Holy of Holies. Only the four garments listed here are suitable for the mission the High Priest was to fulfil inside the Holy of Holies. One of the reasons is that אין קטגור נעשה סנגור, that the accuser cannot also function as the counsel of defence, as we pointed out repeatedly. The presence of gold on the garments of the High Priest would have reminded the attribute of Justice of the episode of the golden calf.

4Alternatively, the reason such garments would not have been in place inside the Holy of Holies is based on Proverbs 25,6: "Do not be boastful in front of a king;" it is bad manners to harp on one's own importance in the presence of G'd Almighty. The words בגדי קודש הם are the Torah's reassurance to us that just these four garments are the sacred vestments suitable for the service about to be described in our chapter. Our sages see in the expression קודש ילבש a reference to where the tunic is to be worn, i.e. inside the Holy of Holies, the place where the Holy Presence of G'd resides. The apparent repetition בגדי קודש הם mean that all of these garments are to be the property of the Temple treasury. (Torat Kohanim).