https://www.heritage.org/constitution/#!...ior-clause
"...ARTICLE III, SECTION 1
The Judges, both of the supreme and inferior Courts, shall hold their Offices during good Behaviour....
The Framers firmly believed that republican liberty could be secured only under the rule of law, and that the rule of law could not be guaranteed without an independent judiciary. The Good Behavior Clause of Article III anchors judicial independence by protecting judges from being removed at the whim of the other branches.
Guaranteed life-tenure for judges had become the rule in England after the Act of Settlement in 1701, though it did not come fully into effect until 1760. Prior to that time, many (including the crown) regarded the “king’s courts” as attached to the executive branch. But as William Blackstone summarized the law in his Commentaries on the Laws of England (1765–1769), “In this distinct and separate existence of the judicial power, in a peculiar body of men, nominated indeed, but not removeable at pleasure, by the crown, consists one main preservative of the public liberty.”
It was different in the colonies. Judges did not have same independence from the crown as they were coming to have in England, leading to the complaint in the Declaration of Independence, “He has made Judges dependent on his Will alone, for the tenure of their offices. . . .” John Adams, wielding great influence during the Second Continental Congress, had pressed for judicial independence. In his Thoughts on Government (April 1776), he urged that judges “should hold estates for life in their offices; or, in other words, their commissions should be during good behavior....""