When Marlow says in heart of darkness,"my speech or my silence,indeed any action of mine , would be a mere futility,"what does he mean ??

There is a sense of futility and existential angst that Marlow feels on this trip. As they float into the heart of darkness, Marlow questions the European presence in the Congo: he questions his presence in the Congo. This steamer itself, close to breaking down, is a metaphor of the psyche of the Europeans heading forward into the jungle.