Final answer:
Justice Brennan cited earlier points of law in his opinions to align with precedent and illustrate how legal interpretations evolve, thereby legitimizing the Court's decision-making process and acknowledging societal changes.
Step-by-step explanation:
Justice Brennan cited earlier points of law in his opinions to ground his reasoning within the precedent set by previous rulings and to illustrate the evolution of legal interpretation. For example, Brennan's view that the Constitution is a "living" document suggests that judges should interpret the constitutional text in a manner that acknowledges the changing understandings of society, such as the evolving concept of equality. This is in line with the principles of stare decisis, which mandates that cases with similar facts should be decided consistently unless there is a justification for a departure. Brennan would thus reference earlier decisions such as Brown v. Board of Education, which marked a significant turn from Plessy v. Ferguson, to emphasize how the Supreme Court's understanding of equality has developed over time. Furthermore, citing precedent also underlines the legitimacy of the Court's rulings, as it shows continuity and respect for the legal process, even as interpretations may shift with new social and legal challenges.