She argued that reforms in a bourgeois system are to be understood as stepping stones towards social revolution, tools to help organize the working class into revolutionaries by showing them what’s possible when their organized.

The thesis is the first paragraph of the introduction:

At first view the title of this work may be found surprising. Can the Social-Democracy be against reforms? Can we contrapose the social revolution, the transformation of the existing order, our final goal, to social reforms? Certainly not. The daily struggle for reforms, for the amelioration of the condition of the workers within the framework of the existing social order, and for democratic institutions, offers to the Social-Democracy the only means of engaging in the proletarian class war and working in the direction of the final goal—the conquest of political power and the suppression of wage labour. Between social reforms and revolution there exists for the Social Democracy an indissoluble tie. The struggle for reforms is its means; the social revolution, its aim.

She however explicitly criticizes Bernstein and other opportunists for assuming that reforms are the be all end all of revolution. Opportunists at the time (and today) argued that a socialist soceity could be built by continuous reforms in the bourgeois political system until eventually you reform out ant vestige of capitalism.

Luxembourg points out why this is impossible and how we must use reforms to further the revolutionary struggle.