How did the Bill of Rights go from being (almost) insignificant to being a powerful set of civil liberties protections?

The Bill of Rights, comprised of the first 10 amendments to the Constitution, was proposed by states to impose limits on federal power and was ratified in 1791. The Bill of Rights became significant as the Supreme Court used these amendments and the protections they include to define the liberties that are enjoyed by Americans.
There are many landmark Supreme Court cases involving the Bill of Rights. For example, the Bill of Right's protections in criminal cases were involved in the Powell v. Alabama (1932) case in which the Supreme Court ruled that indigent clients in capital cases must be provided with counsel at the public's expense. In Mapp v. Ohio (1961), the court ruled that evidence gathered while violating the suspect's rights against unreasonable search and seizure could not be used in a trial (this is the basis of the "exclusionary rule"). In Miranda v. Arizona (1966), the court ruled that people taken into legal custody must be informed of their rights, which are called "Miranda rights." In other words, many Supreme Court cases established civil liberties that the police must grant to suspects in criminal cases and that courts must follow when trying alleged criminals.
Other Supreme Court cases established precedents that protect the right to assembly, granted in the First Amendment. For example, in Dejonge v. Oregon (1937), the Supreme Court granted federal protection of the right of peaceful assembly to the states. In NAACP v. Alabama (1958), the Supreme Court struck down an Alabama law that required organizations to publicly reveal who their members were. Other Supreme Court cases relate to freedom of the press, freedom of speech, freedom of petition, and personal liberties. It was the Supreme Court that over the centuries turned the Bill of Rights into a powerful protection of civil liberties. 
https://billofrightsinstitute.org/educate/educator-resources/landmark-cases/