The 68th prohibition is that [even] a kohen gadol may not always enter the Temple, due to its exalted status and the awe of the Divine Presence.

The source of this prohibition is G‑d's statement1 (exalted be He), "He [Aaron] may not always enter the Sanctuary."

There are various categories within this prohibition: a kohen gadol may not enter the Holy of Holies even on Yom Kippur, except for times designated for the service.2 Similarly, a regular kohen may not enter the Temple building (heichal) the entire year, except for when he is performing the Temple service.

In summary, this prohibition says that if not performing the Temple service, a kohen may not even enter an area he would be allowed to enter, and at a time he would be allowed to enter, unless he is performing a Temple service — whether a kohen gadol inside the Holy of Holies or a kohen outside.3

The punishment for entering such an area without performing the Temple service [varies]: if he entered the Holy of Holies, there is a [Divine] death penalty. If he entered the Temple building (heichal), he receives lashes.

In the words of the Sifra: "The phrase 'He may not always enter' refers to Yom Kippur [— that he may not enter except for the designated times]. The phrase 'the Sanctuary' comes to include the rest of the year. The phrase 'from inside the partition' comes to include the rest of the Temple.4 One might think that the death penalty applies to the entire Temple — therefore the verse adds '[from inside the partition] which faces the Ark, so that he shall not die.' This means that [for entering the area] which faces the Ark [i.e., the Holy of Holies] the penalty is death, but [entering] the rest of the Temple is only a prohibition." Our Sages stated clearly in tractate Menachos,5 "One who enters the Temple building receives 40 lashes."