"Religion is the opium of the people,' said Karl Marx. It is the task of the Communist Party to make this truth comprehensible to the widest possible circles of the labouring masses. It is the task of the party to impress firmly upon the minds of the workers, even upon the most backward, that religion has been in the past and still is today one of the most powerful means at the disposal of the oppressors for the maintenance of inequality, exploitation, and slavish obedience on the part of the toilers.
Many weak-kneed communists reason as follows: 'Religion does not prevent my being a communist. I believe both in God and in communism. My faith in God does not hinder me from fighting for the cause of the proletarian revolution.'
This train of thought is radically false. Religion and communism are incompatible, both theoretically and practically.
Every communist must regard social phenomena (the relationships between human beings, revolutions, wars, etc.) as processes which occur in accordance with definite laws. The laws of social development have been fully established by scientific communism on the basis of the theory of historical materialism which we owe to our great teachers Karl Marx and Friedrich Engels. This theory explains that social development is not brought about by any kind of supernatural forces. Nay more. The same theory has demonstrated that the very idea of God and of supernatural powers arises at a definite stage in human history, and at another definite stage begins to disappear as a childish notion which finds no confirmation in practical life and in the struggle between man and nature. But it is profitable to the predatory class to maintain the ignorance of the people and to maintain the people's childish belief in miracles (the key to the riddle really lies in the exploiters' pockets), and this is why religious prejudices are so tenacious, and why they confuse the minds even of persons who are in other respects able."
"In practice, no less than in theory, communism is incompatible with religious faith. The tactic of the Communist Party prescribes for the members of the party definite lines of conduct. The moral code of every religion in like manner prescribes for the faithful some definite line of conduct. For example, the Christian code runs: 'Whosoever shall smite thee on thy right cheek, turn to him the other also.' In most cases there is an irreconcilable conflict between the principles of communist tactics and the commandments of religion. A communist who rejects the commandments of religion and acts in accordance with the directions of the party, ceases to be one of the faithful. On the other hand, one who, while calling himself a communist, continues to cling to his religious faith, one who in the name of religious commandments infringes the prescriptions of the party, ceases thereby to be a communist."
There you have it.