Yehezkiel 42:20

42:20 He measured it on all four sides. It had a wall around it, 875 feet long and 875 feet wide, to separate the holy and common places.

Yehezkiel 44:23

44:23 Moreover, they will teach my people the difference between the holy and the common, and show them how to distinguish between the ceremonially unclean and the clean. ¹ 

[44:23]  ¹ sn This task was a fundamental role of the priest (Lev 10:10).