Final answer:
Congress wanted a written Declaration of Independence primarily to secure foreign aid and provide a clear rationale for independence. It articulated Enlightenment principles and grievances against British rule, essential for establishing the new nation's moral foundation.
Step-by-step explanation:
The main reason Congress wanted a written Declaration of Independence was rooted in the goal of securing aid from foreign nations during the revolutionary conflict. In addition to the desire for international support, there was an inherent need to articulate a clear rationale for independence both to unify the colonists and to establish the philosophical and moral grounds for the new nation. Thomas Paine's influential pamphlet 'Common Sense' catalyzed a shift in public opinion, aiding the sentiment for independence and setting the stage for the unanimous authorization of the Declaration aside from New York's initial delay.
The Declaration of Independence encapsulated Enlightenment principles, especially the ideas of John Locke, asserting the colonists' right to establish a government based on the consent of the governed. It was crucial to codify these emerging views in a formal document, which also outlined grievances against King George III and justified the pursuit of sovereignty.