Well first lets look into what Prosperity- it is to well prosper- to gain and gain- to have a longevity and an amount that fully just fills one up. So if your prosperous usually you can live in comfort with many things at your side.
If your country is prosperous, it changes your needs, you don't have to worry about lets say materials, so you can create and mass-produce at large so now you have more product for people to buy off of- the more prosperous the more people can flourish and reproduce creating more population- Prosperity can affect peoples lives on many levels of different aspects- from economy, life, medicine, etc. (medicine being able to produce more medicines for the living population to help keep the population alive).
So all in all it increases wellness in people as a whole and therefore creates more opportunities and wellness in general
