Section two, on 'Spontaneity of the masses' is the part where he says that spontaneously, i.e. without the party, the working class will never attain any higher consciousness than that of militant trade unionism. Revolutionary consciousness will only come from outside the day-to-day struggles, i.e. through a party.
In section three, he argues that the Rabochye Dyelo faction are 'economists' meaning that they bow down before the spontaneous trade union consciousness of the masses. He says that they are adding nothing new to the workers' own trade union organisations, and merely reproducing their efforts to no effect. To advance from trade union struggle, to revolutionary consciousness, Lenin is saying, means challenging their existing level of consciousness, not just repeating it back to the workers.