Here's why:
* Impecuniousness is an unfamiliar word for most readers.
* The sentence directly describes the condition of the person being "rags" – this provides a clear definition of the meaning of "impecuniousness" (meaning poverty or lack of money).
Therefore, the phrase "rags he was wearing" acts as a definition clue to help understand the meaning of the unfamiliar word "impecuniousness."