the man who has thought for years in Marxian categories may find it as hard to explain them to simple people as an electrical engineer would find it to explain the theory of turbines to men in a candle-lighted world.

I would somewhat disagree with this. The ideas and concepts aren't that difficult to grasp, it's just the language that is loaded or old or unused by other people. No one thinks of their employer as their "bourgeois", it's their employer! I often substitute words like that, bourgeois -> employer, owner, bourgeoisie -> the owning class, proletariat -> the working class etc. Granted these aren't well defined marxist categories but when explaining stuff like what a Dictatorship of the Bourgeoisie is and how it operates peoples eyes glaze over when you use either "Dictatorship" or "Bourgeoisie". When I say that we are "ruled by the owning class" however that is so self-evident it doesn't even get questioned, opening the possibility of explaining in what way it directly manifests in our life. There is some translation work there and terms might not match up 100% so having multiple terms ready is useful.

Not that I'm some super Marxist buff, I have barely read the basics and not even all of them, but I maintain that if you can't explain something simply you haven't really understood it. I once explained (the general gist of) differentiation to someone using nothing but the rule of three. This requires one to understand a lot of related concepts and clearly, how the rule of three is linked to linear functions, how linear functions are linked to differentiation and how point-wise convergence can be made into a function. Very basic stuff for a mathematician but not for someone whos education stopped at the rule of three and explaining it all would take months. However being so proficient you can reconstruct it from first principles however allows one to explain complicated concepts to laymen using the simple tools they already have.

The important thing is that we don't expect people to understand every concept starting from diamat, but good enough to use them. People don't need to know how induction works in order to calculate mortgages over the next n years...