How can you explain the quote ‘The ruling ideas of each age have ever been the ideas of its ruling class’?

The title quote in question is from the Communist manifesto originally published in 1848. This quote was written in the context of Marx and Engels explaining their theory of history and how economic forces influence legal and political superstructures. Marx didn’t explicitly explain his theory of history in great detail and as such has been constructed over a variety of different texts. G.A. Cohen’s interpretation of Marx’s theory of history is regarded as having the best account of detail, rigor and precision. Such reconstruction of the theory is based on Marx’s writings within the Preface and The German Ideology. However, his interpretation has faced criticism and isn’t universally accepted in that a surprisingly small role for class struggle(a central concept for Marx’s theory) is contained in his interpretation(Ibid). The implicit role of class struggle omitted from Cohen’s interpretation can be given more prominence as a crucial component of hismat. Class struggle is generated by hismat as the development of history gives way to new economic management and hence new ways of determining class and class interest which naturally come into conflict. This is demonstrated in the class struggle between the revolutionary bourgeoisie and the feudal aristocracy. Technological material conditions and productive forces allowed the bourgeoisie to develop as a class. This adaption of Cohen’s theory presents a combined theory that includes technology, productive forces, and class struggle to be determining forces in historical development. Also, class struggle isn’t mentioned explicitly in the 1859 Preface, however, it is possible that it was omitted in an attempt to deter a police censor(see letter to Annenkov). It is plausible that class struggle is compatible with the theory of history.