Religions are not static, they also are subject to dialectical and historical materialism. The rooting out of feudalistic and capitalistic institutional structures from the religious world, and the solving of more material problems by the secular world under socialism, will change people's relationship to religion, which in turn will change religion further.

I don't see any essential reason communists and religious entities have to step on each other's toes, but in the present a lot of incumbent reactionary power rides on existing religious institutions and formats. We can look to the histories of the socialist experiments to see examples both of the initial crushing of the reactionary religious elements, and later of more nuanced handling so that religious elements that pose little or no threat to the proletarian state are let be.

Communists have the soundest and best demonstrated methods of resolving class struggle that I know of, and I also think the changed relationship to work and leisure under socialism goes a long way to healing the lingering wounds of class society. I really don't know if a niche for spirituality will be left open by a communist society, or if the questions that become religious ones will be addressed satisfactorily before they can grow into aches.

For my part in the present, I use spiritual practice because my class enemies are still supplying me with plentiful wounds and aches, and my local communists are far from big or totalizing enough to have subsumed matters presently understood as spiritual. I'm working with the tools I've got.