On Oct. 7, 1941, the socialist dictator of the Soviet Union, Joseph Stalin, lifted a ban on religion in the empire in order to help boost morale both in the military (which was getting slaughtered by the German war machine) and the general populace (which was starving and getting slaughtered). The lifting of the ban on religion reversed just over two decades of state-sponsored oppression against religious believers and clergymen.
The reasons for the Soviet Union's oppression of religious believers are many and varied, but the main one that stands out is that Lenin and other Bolsheviks, once they wrested power away from their political opponents, set out to remake a society that would be totally atheistic and secular. Without competition from gods, the socialist republics of the Soviet Union could then step in and replace the human need for something higher. Instead of a God, or gods, reverence would be directed towards the state, and the state would be responsible for providing its citizens with meaningful work and a standard of living that was not driven by crass consumerism.