In the excerpt from "The Crisis. Number I," Paine uses figurative language to illustrate his unwavering belief that the colonists must fight for freedom. The phrases "little minds to shrink" and "heart is firm" suggest a clear distinction between those who are afraid and those who are steadfast in their principles. Additionally, the metaphor of reasoning being "as straight and clear as a ray of light" emphasizes clarity and determination in his convictions. Therefore, the correct answer is:
D. illustrate his unwavering belief that the colonists must fight for freedom.