Charles Ellicott Commentary Leviticus 16:17

"And there shall be no man in the tent of meeting when he goeth in to make atonement in the holy place, until he come out, and have made atonement for himself, and for his household, and for all the assembly of Israel." — Leviticus 16:17 (ASV)

And there shall be no man. —While the high priest was performing this process of cleansing, no one, whether priest or Israelite, was permitted to be present, thus preventing the possibility of anyone being within the precincts who had unknowingly contracted defilement.

The fact that the high priest was thus alone in the sanctuary, with no one to see how he conducted the ritual, led to the practice of him being sworn by the chief priests and the elders of the Sanhedrin on the eve of the Day of Atonement. He was sworn that he would make no change whatever in the traditional ceremonies of the day, as follows: “We adjure you, by Him who has caused His name to dwell in this house, that you shall not alter anything of all that we say to you.” This had special reference to the points at issue between the Pharisees and Sadducees, as some of the high priests held the Sadducaic views. .