פירוש על במדבר 18:1

ויאמר ה' אל אהרן AND GOD SAID UNTO AARON — i.e. He said it to Moses that he in turn should speak to Aaron to admonish him regarding the precautions to be taken for the benefit of the Israelites in order that they might not enter the Sanctuary (cf. Rashi on Leviticus 1:1 s. v. אליו and Note thereon).

ואתה ובניך ובית אביך אתך תשאו את עון הקודש, you are responsible to prevent unauthorised people, i.e. ritually impure ones and non-priests from entering sanctified domains near the Tabernacle. This is a collective responsibility of all the priests. If unauthorized people nonetheless enter such domains due to inadequate surveillance you will be responsible for such a sin having occurred.

אתה ובניך ובית אביך, "you and your sons, and your father's family." I believe the words ובית אביך refer to Moses, who was also a descendant of Aaron's father, to warn him to observe all the strictures i.e. to prevent unauthorised people from entering the Temple (Tabernacle) precincts. If the word was meant to apply to the Kehatites, in what way were these different from all the other Israelites when it came to entering the Tabernacle? Furthermore, the next verse addresses itself specifically to the Levites which proves that the Torah did not address the Levites in the previous verse. The reason the Torah had to warn Moses was because we learned in Zevachim 102 that the priesthood was never taken away from Moses [after he had performed the sacrificial rites during the first seven days of the Tabernacle's inauguration. Ed.]. Even according to the view that Moses' appointment as a priest was limited to these seven days, I do not believe that he had been forbidden to enter the areas reserved for the priests. Our sages in the Sifri write as follows: "The words בית אביך refer to the Levites; this means that the Levites were instructed by the priests." I believe that this is an halachic exegesis, מדרש הלכה, an attempt to anchor the rules that have been handed down from Sinai in the text somehow.