Refer to the passage. And it proves, in the last place, that as liberty can have nothing to fear from the judiciary alone, but would have every thing to fear from its union with either of the other departments; that as all the effects of such a union must ensue from a dependence of the former on the latter, notwithstanding a nominal and apparent separation; that as, from the natural feebleness of the judiciary, it is in continual jeopardy of being overpowered, awed, or influenced by its coordinate branches; and that as nothing can contribute so much to its firmness and independence as permanency in office, this quality may therefore be justly regarded as an indispensable ingredient in its constitution, and, in a great measure, as the citadel of the public justice and the public security.

–Federalist, no. 78,
Alexander Hamilton

According to Hamilton, why is it necessary to give federal judges "permanency in office”?

to prevent the judicial branch from being dominated by the other branches
to ensure that the judicial branch can control the other branches
to grant the judicial branch powers not designated in the Constitution
to allow the judicial branch to coordinate with the other branches