How did Aaron have to begin his role as high priest compared to how Christ entered?
Aaron began his role by washing thoroughly for complete physical cleansing, putting on holy garments, and offering a bullock for his own sin and household, because he was a sinner. Christ, by contrast, entered sinless, though He took our sin upon Himself.
Les teaches that before Aaron could begin the Day of Atonement, he had to start by washing—wash and wash and wash—with running water, much like surgeons preparing for surgery, depicting a complete physical cleansing. Only then could he put on linen undergarments and holy garments. He then took two young goats and a ram, and in verse 6 offered his bullock as a sin offering for himself and his house, because even as high priest he was a sinner. Les contrasts this with Christ, who went in sinless even though He took our sin upon Himself, so Aaron had to kill the first sacrificial animal for himself and his family.