Agama adalah candu

Religion is the opium of the people: this saying of Marx is the cornerstone of the entire ideology of Marxism about religion. All modern religions and churches, all and of every kind of religious organizations are always considered by Marxism as the organs of bourgeois reaction, used for the protection of the exploitation and the stupefaction of the working class.
atau diterjemahkan:
Agama adalah opium bagi masyarakat: ini tulisan Marx, inilah batu loncatan dari keseluruhan ideologi Marxisme mengenai agama. Seluruh agama dan gereja-gereja modern, semua jenis organisasi agama selalu dianggap organ dari reaksi borjuis oleh Marxisme. Ia digunakan untuk melindungi eksploitasi dan kelumpuhan kelas pekerja
Hanya saja , meskipun Lenin kritis terhadap agama, ia membuat kesimpulan untuk tidak memasukannya dalam "Program Kita" atau sasaran ideologinya dengan mengatakan:
But under no circumstances ought we to fall into the error of posing the religious question in an abstract, idealistic fashion, as an “intellectual” question unconnected with the class struggle, as is not infrequently done by the radical-democrats from among the bourgeoisie. It would be stupid to think that, in a society based on the endless oppression and coarsening of the worker masses, religious prejudices could be dispelled by purely propaganda methods. It would be bourgeois narrow-mindedness to forget that the yoke of religion that weighs upon mankind is merely a product and reflection of the economic yoke within society. No number of pamphlets and no amount of preaching can enlighten the proletariat, if it is not enlightened by its own struggle against the dark forces of capitalism. Unity in this really revolutionary struggle of the oppressed class for the creation of a paradise on earth is more important to us than unity of proletarian opinion on paradise in heaven.