A panacea; a scheme to bring about some promised reform; a beau ideal. Of course the theological word is the Anglo-Saxon godspell, i.e. God and spel (a story), a translation of the Greek evangelion, the good story.
“Mr. Carnegie's gospel is the very thing for the transition period from social heathendom to social Christianity.” —Nineteenth Century (March, 1891, p. 380).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894