My understanding of this is: They attach greater significance to the ways people see their objective situation, to the significance of ideology, (to the) struggle between classes in the realm of cultural production, and (to) the production of symbolic meanings as active forces in historical change. The "struggle" is between classes in the realm of cultural production. "The production of symbolic meanings" means just that: people produce symbolic meanings of various kinds and these symbolic meanings can become forces for historical change.
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