The revival camp meeting in the novel works on several levels. The most obvious fact at work is the fact that the King is cynically playing upon the emotions of the gathering.
These people have purportedly gathered together to save their souls; find salvation, etc. The King sees the vulnerability that this effort conveys to the gathering and takes advantage of it.
This episode also carries a subtle implication that the salvation the gathering is seeking is self-serving, superficial and foolish. The crowd is certainly easily fooled by the King's impromptu yarn. Importantly, they are also highly satisfied by it.
The King's act effectively stops the salvation, speaking in tongues, and other effects of the revival, replacing them with a shaky concept of charity. How could a truly fervent group be so easily persuaded and led away from its aim? The answer is that the group must have been less fervent than it purported to be.