Albert Barnes Commentary Leviticus 16:2

"and Jehovah said unto Moses, Speak unto Aaron thy brother, that he come not at all times into the holy place within the veil, before the mercy-seat which is upon the ark; that he die not: for I will appear in the cloud upon the mercy-seat." — Leviticus 16:2 (ASV)

The holy place within the veil — See Exodus 26:33-34; Hebrews 9:3.

The cloud — Compare Exodus 16:10 note.

The mercy seat — See Exodus 25:17 note.