When one of the other priests died, he could not continue being a priest. So there were many priests.
But because Jesus lives forever, he will never stop serving as priest.
So he is able always to save those who come to God through him because he always lives, asking God to help them.
Jesus is the kind of high priest we need. He is holy, sinless, pure, not influenced by sinners, and he is raised above the heavens.
He is not like the other priests who had to offer sacrifices every day, first for their own sins, and then for the sins of the people. Christ offered his sacrifice only once and for all time when he offered himself.
The law chooses high priests who are people with weaknesses, but the word of God's oath came later than the law. It made God's Son to be the high priest, and that Son has been made perfect forever.