Heb 10:1-3 The Torah has in it shadows of good things yet to come, not the very image of those things. That is why a slaughter which the high priests offered once a year (Lev 16:34) could not make those who draw near (the high priests, who were themselves only a "shadow of a good thing to come", Deu 21:5; Lev 10:1-3 & Lev 16:1-2; Heb 3:1) of full age (Heb 7:23-24). For then would a slaughter not have ceased to be offered? Because those servants (the high priests) once purged (Heb 9:14), should have had no sense of mortality. But in a slaughter there is a reminder of their sins every year (Heb 9:7 & Eze 18:4).
The Abrabanel (Don Isaac Abrabanel of Spain, 1437-1508) reminds us of the significance of the death of a high priest: "The high priest was a prince and a leader of Israel and was consecrated to God. Upon his death the whole nation would tremble and the living would recognize that the days of man are like a shadow".