Class is A Material Difference Based On A Social Relation

To abolish the social relation you must abolish the material difference (E.G. You must abolish private property.)  All other axes of oppression are social relations based on some random (often vague) material difference, and the material difference can be left alone (E.G.. You do not need to abolish people having different skintones and hair textures to abolish the social relation of race)