For those uninitiated, Prosperity Gospel is the Biblically dubious concept taught at many evangelical churches that god bestows material wealth on those whom he favors. Generally, this is with the explicit instruction that one must tithe to the church in order to receive the lord's good will. Typically, church leaders who espouse this philosophy become very wealthy on the largesse of their congregation and then use this wealth as a validation of this same policy.
This teaching, that one's worldly life will be improved by devotion, strikes me a symptom of the weakening of faith on a mass scale. The congregants of such churches, whether they realize it or not, don't really believe in afterlife rewards anymore. Salvation isn't enough anymore. The promise of heaven seems empty so religious institutions need to make more immediate promises in order to recruit and retain followers. They must sell religion as an investment scheme rather than a path to enlightenment.
There was a time when Xians were supposed to be absolutely contemptuous of worldly things. God could shit on you your whole life just to see if you'd remain faithful as he did to Job and no reward could be expected while one was on Earth. Poverty brought one closer to grace. The meek shall inherit, camels through the eyes of needles and all that.
No one in Evangelical America believes this anymore, of course. They may say that they do and might even believe it but, like all the business of religion, simply believing it does not make it true. The poster children for todays Xianity are rockstars that make fantastic amounts of money. Mega-churches are palaces that rival sports stadiums in size and multiplexes in comfort. The pastors at these churches often make six figures or more and they promise likewise to the most devoted from their flock.
In today's America, faith has become a ponzi scheme because greed sells better than God, himself