Final answer:
The "House Divided" speech is named for its powerful metaphor illustrating the nation's division over slavery, indicating a future where the U.S. would have to become entirely free or entirely slave-owning.
Step-by-step explanation:
Lincoln's June 15, 1858 speech at Springfield, Illinois, is commonly referred to as the "House Divided" speech because it addressed the critical issue of whether the United States could continue to exist as a nation divided between slave states and free states.
Lincoln eloquently cautioned that 'A house divided against itself cannot stand...this government cannot endure, permanently, half slave and half free'.
This statement signified Lincoln's stance on slavery and foreshadowed the eventual necessity for the nation to be unified under either freedom for all or slavery extended across all states, encapsulating the sectional crisis and the intense political and moral questions of the time.
During this period, the divide over slavery was exacerbating tensions within the country, especially after the Dred Scott decision and the Kansas-Nebraska Act, which raised fears that slavery could be extended into northern territories.
These issues, along with others, dominated the Lincoln-Douglas debates where Lincoln's arguments reinforced the Republican Party's stance against the expansion of slavery. Although Lincoln lost the Senate race to Douglas, his voiced principles during the debates raised his national profile and set the stage for his future Presidential election.