How was Christ's entry as high priest different from Aaron's?
Christ entered as high priest sinless, even though He took our sin upon Himself. Aaron, by contrast, was a sinner like everyone else, so he first had to wash thoroughly, put on holy garments, and offer a bullock as a sin offering for himself and his house before he could begin his high priestly role.
Les explains that Aaron, as high priest of Israel, still had to start the Day of Atonement by washing and washing and washing in running water—almost as surgeons prepare for surgery—to depict a complete physical cleansing. Only then could he put on the linen undergarments and holy garments. In verse 6, Aaron had to offer his bullock of the sin offering for himself and his house, because even though he was high priest, he was a sinner and sinned just as well as anybody else. Les points out that this is where Christ differs: Christ went in sinless, even though He took our sin upon Himself. Aaron, however, had to kill the first sacrificial animal for himself and his family before proceeding with the blood and the altar of incense.