None of this happened without an oath. The men from the tribe of Levi may have become priests without an oath,
but Jesus became a priest when God took an oath. God said about him, "The Lord has taken an oath and will not change his mind. You are a priest forever."
In this way Jesus has become the guarantee of a better promise.
There was a long succession of priests because when a priest died he could no longer serve.
But Jesus lives forever, so he serves as a priest forever.
That is why he is always able to save those who come to God through him. He can do this because he always lives and intercedes for them.
We need a chief priest who is holy, innocent, pure, set apart from sinners, and who has the highest position in heaven.
We need a priest who doesn't have to bring daily sacrifices as those chief priests did. First they brought sacrifices for their own sins, and then they brought sacrifices for the sins of the people. Jesus brought the sacrifice for the sins of the people once and for all when he sacrificed himself.
Moses' Teachings designated mortals as chief priests even though they had weaknesses. But God's promise, which came after Moses' Teachings, designated the Son who forever accomplished everything that God required.