Question

What is the main purpose of the final sentence in the excerpt from Thomas Paine's Common Sense?

Answer 1

Based on the sentence of the excerpt,
The main purpose of the final sentence from Thomas Paine's common sense would be :
To indicate that the American colonies can establish a better government thana  monarchy

Hope this helps

Answer 2

The main purpose of this last sentence is to convince the colonists of rising up to the challenge of independence, and of creating a new government in America. Paine hopes that by highlighting the importance of legacy he will be able to convince the colonists of his view. He tells them how, if they try to shirk from doing what they must, future generations will think of them in a hateful way (detestation) for missing the chance to improve society.