The judicial component of government is independent in order to insulate its members from punitive or coercive actions by the legislative and executive departments of the government. If the judiciary is independent, then it can make fair decisions that uphold the rule of law, an essential element of any genuine constitutional democracy.
The U.S. Constitution, for example, protects judicial independence in two ways. First, Article III says that federal judges may hold their positions “during good Behaviour.” In effect, they have lifetime appointments as long as they satisfy the ethical and legal standards of their judicial office. Second, Article III says that the legislative and executive branches may not combine to punish judges by decreasing payments for their services. The constitutions of some democratic countries provide appointments to the judges for a specific period of time, but invariably they protect their independence of action during their terms of office.
Alexander Hamilton, a framer of the U.S. Constitution, offered justification for an independent judiciary in the 78th paper of “The Federalist.” He wrote, “The complete independence of the courts of justice is peculiarly essential in a limited Constitution.” Hamilton claimed that only an independent judicial branch of government would be able to impartially check an excessive exercise of power by the other branches of government. Thus, the judiciary guards the rule of law in a constitutional democracy. – John Patrick, Understanding Democracy, A Hip Pocket Guide