How was Christ's entrance into His role different from Aaron's?
Christ entered His role sinless, though He took our sin upon Himself, whereas Aaron was a sinner who first had to kill a sacrificial animal for himself and his family. Aaron also had to wash and put on holy garments before serving, but Christ needed no cleansing.
Les explains that Aaron, as high priest of Israel, was still a sinner and sinned just as anyone else. Before he could begin the day of atonement, he had to wash thoroughly—almost like a surgeon preparing for surgery—depicting complete physical cleansing, then put on linen undergarments and holy garments. He then had to offer his bullock as a sin offering for himself and his house. By contrast, Christ went in sinless, even though He took our sin upon Himself. Aaron had to kill that first sacrificial animal for himself and his family, but Christ did not need to make atonement for Himself.