Selective Incorporation and Free Speech

In the context of the U.S. legal system, the principle of selective incorporation is essential for understanding how certain amendments in the Bill of Rights have been applied to state laws through the Fourteenth Amendment. The process ensures that fundamental rights are protected from infringement by state governments as well as the federal government. Considering its application, which of the following Supreme Court cases was pivotal in the incorporation of the First Amendment's freedom of speech clause against the states?