The final paragraph of Swift's "A Modest Proposal," first, serves the usual purpose of a final paragraph in an essay by providing the conclusion. He summarizes the benefits of his proposal, for instance:
- it's for the public good
- will advance trade
- will provide for infants
- will relieve the poor of their poverty
- will give some pleasure to the rich
Beyond that, the final paragraph establishes that the speaker is not making this proposal so that he can profit financially from it. He has no children that are not already too old, and his wife is past child-bearing age.
In general, in addition to these specifics, the paragraph contributes to the irony of the piece, as well as the humor. The speaker presents his proof that he is not trying to get rich off of his proposal as if it is a serious proposal, continuing the irony used throughout the piece.