Hebrews 7:23-24

‘And they indeed have been made priests many in number, because that by death they are hindered from continuing, but he, because he abides for ever, has his priesthood unchangeable.’

Again the point is drawn out that the levitical priests were numerous and constantly changing because death prevented them from continuing. There was constant fluctuation. But He on the other hand continues on permanently. He abides for ever. Therefore His priesthood is unchanging, and there can thus be no argument about the superiority of the new priesthood and the new covenant, for they are eternal.