Question

read the excerpt from president roosevelts state of the union address. i cannot prophesy. i cannot tell you when or where the united nations are going to strike next in europe. but we are going to strike—and strike hard. the primary purpose behind roosevelts words in this excerpt is to impress the public with emotional diction. inspire the public to join the military. convince the public of americas strength. encourage viewers to remain active.

Explanation:

Roosevelt is emphasizing that the United Nations will strike hard, which aims to show America's strength (as a major part of the United - Nations forces at the time). The tone is assertive about future action rather than using emotional diction just for the sake of impressing, there's no mention of joining the military, and no call for remaining active in a general sense.

Answer:

convince the public of America's strength.