Why did the high priest have to sacrifice for his own sin before the Day of Atonement?
Aaron had to offer a bullock as a sin offering for himself and his household because, though he was Israel’s high priest, he was still a sinner who sinned like everyone else. This sacrifice was necessary before he could begin the Day of Atonement ministry, prefiguring Christ, who entered sinless.
Les explains that before Aaron could begin the Day of Atonement ritual, he first had to wash and wash, using running water, depicting a complete physical cleansing. Only then could he put on the linen undergarments and the holy garments. In verse 6, Aaron was to offer his bullock of the sin offering for himself and his house. Even though he was the high priest of Israel, he was a sinner and sinned just as well as anybody else. Therefore, to even begin this role, Aaron had to kill the first sacrificial animal for himself and his family. Les contrasts this with Christ, who went in sinless, even though He took our sin upon Himself. After that, the high priest would take the blood of the offering, stop at the cleansing, and bring coals to put on the altar of incense, whose smoke served as his protection or covering.