There are cottage industries of academics living of the questions such as what did Marx actually say, or what did Keynes really mean? A sign that you have really made it is people squabbling over what you really said.
Stigler’s law of textual exegesis (1965) is that because even the great and the good are human enough to contradict themselves, change their minds, and even write in vague terms from time to time and are misheard, rely on their own summaries of their own work to work out what they really think rather than hand-picked quotation. You can then check if their analytical system supports their summaries of their main work:
Let us recognize the fact that the interpretation of a man’s position –– especially if the man has a complex and subtle mind –– is a problem in inference, not to be solved by the choice of quotations.
As for why we ponder over the great texts, our goal should not be to understand what an author really believed, instead it is
…to maximize the value of a theory to the science… The man’s central theoretical position is isolated and stated in a strong form capable of contradictions by facts. The net scientific contribution, if any, of a man’s work is thus identified, amended if necessary, and rendered capable of evaluation and possible acceptance.