He was then told to cut the sacrificial goat and sprinkle its blood over a cover in front of a cover. He now had to perform a sacrifice in atonement for the sins of his sons, by taking a bull and sprinkling its blood exactly how he had done for the goat.

Aaron was not told directly by God, but even through Moses his faith was, and would never be broken. “He also told Moses to caution Aaron not to die as his sons died.” (Leviticus 16:1) (Ibn Ezra)This commentary is showing the shame of his sons' sins and the importance of their priestly roles. It is like when a little child sins, they are unable to apologize so the parent must do it. The parent knows they are unable to lecture the small child so they must carry on while setting the appropriate example for their child. This parasha seems simple but the life lessons we can learn from it lie deep within its roots.