John Calvin 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)

Speak unto Aaron. The sum of the law is that the priest should not frequently enter the inner sanctuary, but only once a year, that is, on the Feast of Atonement, in the month of September. The reason for this was so that a more frequent entrance of it would not produce indifference; for if he had entered it indiscriminately at every sacrifice, no small part of the reverence due to it would have been lost.

The ordinary sprinkling of the altar was sufficient to testify to the reconciliation, but this annual ceremony influenced the people’s minds more greatly. Again, by this sacrifice, which they saw only once at the end of the year, the one and perpetual sacrifice offered by God’s Son was more clearly represented.

Therefore, the Apostle elegantly alludes to this ceremony in the Epistle to the Hebrews, where it is said that by the annual entrance of the high priest the Holy Ghost signified,

“that the way into the holiest of all was not yet made manifest, while as the first tabernacle was yet standing,” (Hebrews 9:8).

And a little further on he adds, that after Christ the true Priest had come,

“he entered in once into the holy place, having obtained eternal redemption for us” (Hebrews 9:11–12).

Thus the year, in the ancient type, was a symbol of the one offering, so that believers might understand that the sacrifice by which God was to be propitiated was not to be often repeated.

So that God may inspire greater fear and preserve the priests from carelessness, He proclaims that His glory should appear in the cloud in that part of the sanctuary where the mercy seat was. For we know that the sign was given from there to the Israelites, when the camp was to be moved or when they were to remain stationary.

But this testimony of God’s presence should have justly moved the priests to greater care and attention. And from this we may now learn that the closer God’s majesty manifests itself, the more anxiously we should beware, so that we do not, through our thoughtlessness, give any mark of contempt, but rather that we should testify to our submission with becoming humility and modesty.