Final answer:
Roosevelt's speech aimed to address the danger to the United States after Pearl Harbor and persuade Congress to declare war on Japan. It symbolized a shift from neutrality to active participation in World War II and reflected Roosevelt's earlier stance on supporting the Allies.
Step-by-step explanation:
The phrase that best describes Roosevelt's purpose for making the speech is to address a potential danger to the security of the United States. President Franklin D. Roosevelt's speech, given in the aftermath of the devastating attack on Pearl Harbor, served to both inform Congress and the American people of the events, and to persuade Congress to declare war against Japan, thereby bringing the United States into World War II. The speech, known for its famous line 'a date which will live in infamy,' was carefully crafted using rhetorical devices that emphasized the surprise and calculated nature of the attack, urging the country to take action.
Although the United States had officially remained neutral in World War II until the attack, Roosevelt had been advocating for support of the Allies against the aggressions of Germany and Japan. His private communications and actions suggested a growing desire to aid Britain and France, indicating that while he publicly maintained a stance of neutrality, he believed in the potential of the U.S. to serve as an arsenal of democracy. This dual approach reflected a complex interplay between the noninterventionist sentiments within Congress and Roosevelt's leadership in the face of global threats.