Hebrews 7:23

23 Now there have been many of those priests, since death prevented them from continuing in office;

Read Hebrews 7:23 Using Other Translations

And they truly were many priests, because they were not suffered to continue by reason of death:
The former priests were many in number, because they were prevented by death from continuing in office,
There were many priests under the old system, for death prevented them from remaining in office.