Final answer:
Thomas Paine's writing aimed to motivate the colonists to persevere in their struggle for freedom against the British, emphasizing the moral and divine righteousness of their cause.
Step-by-step explanation:
The author's purpose in writing the excerpt from Crisis No. 1 by Thomas Paine was to inspire and encourage the colonists to stand firm in their fight against British tyranny during the American Revolution. Paine's use of powerful and motivational language was meant to rally the American colonists by depicting the struggle for independence as both a duty and a test of character. He contrasts the 'summer soldier and the sunshine patriot' with those who persist through hardships, deserving gratitude and love. He also highlights the oppressive nature of British rule and equates the unlimited power Britain claimed to have over the colonies to divine authority, which should only belong to God. This serves to strengthen the moral stance against British rule and galvanizes the colonists to continue their pursuit of freedom.