Why did Aaron have to wash his body and put on clean linen garments?

Les explains that Aaron could come into the holy place behind the veil with a young bullock for a sin offering and a ram for a burnt offering, but he did not take the animal; he took only the blood. In verse 4, Aaron was to put on the holy linen coat, linen breeches, linen girdle, and linen miter. Les points out that linen in Scripture speaks of righteousness and cleanliness. These were holy garments, so Aaron had to wash his flesh in water and put them on. Not only was his clothing impeccable, not a spot or wrinkle, but his own flesh also had to be washed so everything was impeccably clean. Les says this speaks of our high priest in the same way: He was clean, without spot, without blemish. Aaron also offered his bullock of the sin offering for himself and made atonement, a covering, for himself and his house.