Whose sin offering did Aaron offer first on the Day of Atonement?
Aaron first offered his own bullock as the sin offering, making atonement for himself and his house. Even though he was high priest of Israel, he was a sinner and had to be cleansed before he could begin the Day of Atonement rituals.
Les explains that Aaron, as high priest, first had to wash and put on the holy linen garments. Then he was to take two goats from the congregation—one for a sin offering and a ram for a burnt offering. But before dealing with the people's offering, verse 6 says Aaron shall offer his bullock of the sin offering, which is for himself, and make atonement for himself and for his house. Les points out that even though Aaron was high priest of Israel, he was a sinner just like everyone else. So he had to kill this first sacrificial animal for himself and his family before he could begin his role. This contrasts with Christ, who went in sinless, even though He took our sin upon Himself.
And Aaron shall offer his bullock of the sin offering, which is for himself, and make an atonement for himself, and for his house.