Jesus is the high priest… The priesthood of the former (and current) priests ended (and/or will end) with their death. However, Jesus Christ lived after death so His priesthood continues.
In addition, Christ have the oath from God. The other priests didn’t/don’t have Yahweh’s oath.
“And inasmuch as it was not without an oath
(for they indeed became priests without an oath, but He with an oath through the One who said to Him, “The LORD HAS SWORN AND will NOT CHANGE HIS MIND, ‘YOU ARE A PRIEST forever'”);
so much the more also Jesus has become the guarantee of a better covenant.
The former priests, on the one hand, existed in greater numbers because they were prevented by death from continuing,
but Jesus, on the other hand, because He continues forever, holds His priesthood permanently.
Therefore He is able also to save forever those who draw near to God through Him, since He always lives to make intercession for them.
For it was fitting for us to have such a high priest, holy, innocent, undefiled, separated from sinners and exalted above the heavens;
who does not need daily, like those high priests, to offer up sacrifices, first for His own sins and then for the sins of the people, because this He did once for all when He offered up Himself.”
~ Hebrews 7:20-27