Friedrich Engels (co-author of The Communist Manifesto) wrote a “Draft of a Communist Confession of Faith”, following a similar Question/Answer format as seen in the Traditional Catholic Catechism and Doinel’s Gnostic Catechism.
While the confession deals mainly with the material conditions of the working classes (as they were in 1847) and a hypothetical communist future, the last question regards religion in an interesting way. While many would assume an outright rejection of religion by communists, the answer Engels puts forward is a bit more nuanced:
“All religions which have existed hitherto were expressions of historical stages of development of individual peoples or groups of peoples. But communism is that stage of historical development which makes all existing religions superfluous and supersedes them.”
While some may disagree with the ideas of Marx and Engels, the idea about a “stage of historical development which makes all existing religions superfluous and supersedes them” is particularly relevant to the idea of Free Illuminism.
If we were to assume the position of Marx/Engels, where history develops in stages (Slavery>Feudalism>Capitalism>Communism), a simultaneous evolution of religion would follow with each of these stages, resulting in a departure from the use of religion to enforce oppressive power structures and serve the agendas of ruling classes, instead shifting to an idea of religion which serves the masses and empowers each individual, thus making “all existing religions superfluous” and superseding them.