Moses
Leviticus 16:2ESV·traditional attribution

and the LORD said to Moses, “Tell Aaron your brother not to come at any time into the Holy Place inside the veil, before the mercy seat that is on the ark, so that he may not die. For I will appear in the cloud over the mercy seat.

John Calvin Reformed @genevareformer

2. Speak unto Aaron. The sum of the law is, that the priest should not frequently enter the inner sanctuary, but only once a year, i.e., on the feast of the atonement, in the month of September. The cause of this was, lest a more frequent entrance of it should produce indifference; for if he had entered it promiscuously at every sacrifice, no small part...

Matthew Henry Presbyterian @wholebiblehenry

Here is, I. The date of this law concerning the day of atonement: it was after the death of the two sons of Aaron (Lev 16:1), which we read, Lev 10:1. 1. Lest Aaron should fear that any remaining guilt of that sin should cleave to his family, or (seeing the priests were so apt to offend) that some after-sin of his other sons should...

Commenting on Leviticus 16:1-4

John Gill Reformed Baptist @doctorgill

And the Lord said unto Moses, speak unto Aaron thy brother,.... Who was the high priest; and what is here said to him was binding on all high priests in succession from him: that he come not at all times into the holy place; or "holiness" (p), which was holiness itself, or the most holy place, as distinguished from that which was sometimes called the...