Source: Georgi Plekhanov, Selected Philosophical Works, Volume 3 (Progress Publishers, Moscow, 1976), pp 98-99. Prepared for the Marxist Internet Archive by Paul Flewers.
Moscow Editor’s Note: ‘In 1907 the journal Mercure de France sponsored a questionnaire consisting of a single question: ‘Assistons-nous à une dissolution ou à une évolution de l'idée religieuse et du sentiment religieux?’ (‘Are we witnessing the dissolution or the evolution of the religious idea and religious sentiment?’) Thirty-three replies were published in no 236 of the journal for 15 April 1907, from political and social figures and writers in various countries, including Maxim Gorky, Strindberg, Vandervelde and Verhaeren.’
You ask: are we witnessing the decay or the evolution of the religious idea and religious feeling?
Allow me to reformulate the question from a social-evolutionary point of view: is not the decay of the religious idea the natural end of its evolution?
To be able to answer this question, let us take into account what the evolution of the religious idea has been up to the present.
But, first of all, what is religion? If we use what Edward B Tylor called ‘a minimum definition of the term religion’, we shall say that religion is belief in spiritual beings existing alongside bodies and the natural processes. 
This belief, which constitutes the necessary element of every religion, serves also to explain all natural phenomena. But at a higher stage of social evolution a new element, namely, morality, joins this original one.
The link between these two elements grows more and more close. Then we come to what I might call ‘a maximum definition of the term religion’: belief in spiritual beings associated with morality and serving as its sanction. This is why the essence of religion for many people is morality.
But we are a long way yet from the end of this evolution.
The seemingly indissoluble link between morality and religion is doomed to disappear as a consequence of the progress of human reason.
The scientific explanation of phenomena can only be materialist. The intervention of spiritual beings may explain phenomena to the mind of a savage, but it explains nothing to the mind of a Berthelot; the significance of such an explanation diminishes for every civilised person in proportion as he assimilates the results of scientific work.
If many people still believe in spirits and supernatural beings, this is because, for various reasons, they have been unable to overcome the obstacles preventing them from adopting the scientific point of view.
When these obstacles have been removed – and there is every reason to believe that social evolution will accomplish this – every trace of supernatural conception will disappear and morality will come into its own. Religion, in the maximum sense of the word, will cease to exist. As regards religious feeling, this too will evidently disappear with the decay of the religious idea. But, of course, there is more conservatism in feelings than in ideas. There may and will be, in all probability, survivals which will produce mongrel, semi-materialist, semi-spiritualist conceptions of the world.
But these survivals too are in their turn doomed to pass away, especially with the passing of some social institutions seemingly sanctioned by religion.
Human progress sounds the death-knell both for the religious idea and for religious feeling. Timid people, or those with a stake in religion, express fears for the future of morality. But, I repeat, morality can have an independent existence.
Belief in spiritual beings even at the present time is very far from being a buttress of morality. On the contrary, the religious beliefs of civilised peoples in our day, in the majority of cases, are lagging behind the moral development of these peoples.
WK Clifford justly remarked: ‘If people were no better than their religions, the world would be a hell.’
Notes are by Plekhanov.
1. True, a spiritual being is not yet a god. To become a god, the spiritual being must complete a certain evolution. God is a spiritual being linked by mutual services with a given tribe or nationality. But every god is a spiritual being. In the present case that is all we need to know.