Charles Spurgeon Commentary Leviticus 16:4

"He shall put on the holy linen coat, and he shall have the linen breeches upon his flesh, and shall be girded with the linen girdle, and with the linen mitre shall he be attired: they are the holy garments; and he shall bathe his flesh in water, and put them on." — Leviticus 16:4 (ASV)

Our great High Priest offered himself without spot to God, and he is himself without sin; but the Jewish high priest must make himself symbolically pure by putting on the snow-white garments of holy service, and before doing so, he must wash himself with water, so that he might come before God acceptably. No one could approach the Holy God with impurities on them.