Why were the Cooper Union Speech in 1860 important?

Abraham Lincoln's Cooper Union speech in 1860 was significant because it effectively articulated the Republican Party's stance against the expansion of slavery into the territories, resonating with a Northern audience. By presenting historical evidence and legal arguments, Lincoln positioned himself as a strong candidate for the presidency, enhancing his national profile. The speech helped to galvanize support for his campaign, ultimately contributing to his election and the ensuing national debates over slavery and states' rights.