It is far better, I think, to be specific on the work of history or theory you're advocating for than to tell others to read a book/learn history/etc. Many such works are integral to destroying the braincage of, for instance, Amerikan exceptionalism.
In a hypothetical conversation wherein I am trying to dissuade someone from engaging in Amerika apologia, I would recommend Rogue State and Killing Hope by William Blum before anything else, while giving them my own thoughts and opinions regarding Amerika's crimes.
Were the issue, say, unconditionally defending the traditional family structure, I would cite Engels' The Origin of the Family. The necessity of the state and the banality of most "anarchism"? On Authority and Anarchism or Socialism? by comrade Ioseb. I would also direct that someone to read these works.
And other works, depending on specificity of issue and political learnedness of the individual being engaged with. If there is a point to my rambling, it's that literally saying "read theory", while potentially a funny (and fair) meme to throw at trolls and bad faith actors, doesn't do much for educating anyone. What theory? I think that's important.
We should be able to understand that theory and history well enough to put it into digestible reality for the working class, of course. But directing others to that theory only strengthens communism's presence in political thought. Those who become educated in said theory will tell others who will tell others. This is good.
And I guess, for honesty's sake and for anyone reading who potentially does the same, I have told others, in the past, to "read theory" without diving into specifics because I did not heed my own advice and thusly could not actually give them specifics. I was being hypocritcal in my posturing, at the time.
It's definitely important to read and understand. It's also incredibly important to treat others with empathy and as fully cognizant beings capable of rational thought, who when guided towards genuine education and not hit with directionless platitudes may actually change their understandings of the world. For the most part, anyway.
It's worth noting that no one expects you, the reader of this, to know everything, nor do you have to. We strive to learn as much as we can, and that is a worthwhile endeavor. Just as worthwhile is putting that knowledge into action.