Earlier there were a lot of priests, for they died and had to be replaced. But Jesus’ priesthood is permanent. He’s there from now to eternity to save everyone who comes to God through him, always on the job to speak up for them.
So now we have a high priest who perfectly fits our needs: completely holy, uncompromised by sin, with authority extending as high as God’s presence in heaven itself. Unlike the other high priests, he doesn’t have to offer sacrifices for his own sins every day before he can get around to us and our sins. He’s done it, once and for all: offered up himself as the sacrifice. The law appoints as high priests men who are never able to get the job done right. But this intervening command of God, which came later, appoints the Son, who is absolutely, eternally perfect.