Or HaChaim on Exodus 28:42/אור החיים על שמות כ״ח:מ״ב

1 ועשה להם מכנסי בד, "and make for them pants of linen, etc." Why did the Torah wait so long with the commandment to make pants for the priests? Inasmuch as the Torah had instructed Moses to dress the priests in their service garments I would have thought that this instruction included the need for Moses to put on their pants. In order for us to know that the priests were to put on the pants themselves, the Torah delayed telling us about the pants until after commanding Moses to put the other garments on Aaron and his sons. We must not conclude from the positioning of this commandment that the pants were the last garment the priests were to put on. The Torah mentions in Leviticus 16,4 that the pants should cover the flesh of the priests, and we learned in Yuma 23 that the pants were the first garment the priests were to put on. Our interpretation of the delay in mentioning the need for the priestly garments to include pants is correct then.

2Another reason for listing the pants as the last of the priestly garments may be the Torah's intention to position this commandment immediately adjacent to the warning in verse 43 for the priests not to become guilty of an iniquity as a result of which they would die. Had the Torah included the commandment for the priests to wear special pants when the other garments were listed, I might have concluded that the warning in verse 43 applied only to the garments other than the pants seeing that the reason the priests had to wear pants was for the sake of chastity, something applicable to every male, not just to priests. By positioning the requirement that the priests were to have special pants to be worn when they performed the service in the Temple, the Torah made it clear that whatever rules applied to the other priestly garments also applied to their pants.