Leviticus 16:4

4. The holy linen coat This requirement, that Aaron should divest himself of his pontifical robes when he appears before the Lord as a penitent, teaches us that no worldly distinction, no ecclesiastical preferment, is of any avail to avert the wrath of God. When Aaron represents God to men he may well be clothed with splendour, but when as a sinner he stands before the divine holiness, that splendour pales. The day of atonement stained the glory of all flesh by the revelation of Jehovah’s holiness in contrast with man’s guilt.

Breeches Properly, drawers. See Leviticus 6:10, note. The high priest is required to appear in the apparel of a common priest, with the addition of a linen mitre, a distinctive badge of the pontificate. This change of raiment represents a humiliation as deep as does the wearing of sackcloth upon the common people.

Wash his flesh It became the typical high priest to be “holy, harmless, and undefiled,”

that he might fitly prefigure the spotless Son of God. It was customary to remove him from his own house to a chamber in the temple seven days before, lest he should contract any defilement which might entail an uncleanness during those seven days, and he be disqualified for his duty on the great day of atonement. During this time he was exercised in all the various parts of the service, though not entering within the veil. The law relating to his duties was read to him again and again, lest he should make any mistake in his office on that day to his own destruction and the detriment of the people. The elders of the Sanhedrin solemnly adjured him in these words: “We adjure thee, O high priest, our delegate, by Him that caused his name to dwell in this house, that thou alter not any thing of what we have spoken unto thee.”- Delitzsch on the Hebrews, Appendix.