The issue is the revolution is not an instant snap to full communism. There will need to be structures in place to prevent the slipping back into capitalism, and the undermining of the new proletarian state by internal and external forces. This means things like police, military, and government, but fundamentally different as the structure of the society they serve will not be designed to protect the wealthy. The transition from revolution to full stateless, classless, moneyless communism will take an unknown amount of time.