Source: How to Read a Book: The Classic Guide to Intelligent Reading (Revised 1972 ed.), p. 284 Top.
Spinoza carried the conception even farther. His Ethics is written in strict mathematical form, with propositions, proofs, corollaries, lemmas, scholiums, and the like. However, the subject matter of metaphysics and of morals is not very satisfactorily handled in this manner, which is more appropriate for geometry and other mathematical subjects than for philosophical ones. A sign of this is that when reading Spinoza you can skip a great deal, in exactly the same way that you can skip in Newton. You cannot skip anything in Kant or Aristotle, because the line of reasoning is continuous; and you cannot skip anything in Plato, [1.] any more than you would skip a part of a play or poem. [End of 1.]
I have not read Plato's or Socrates's (as reported by Plato) œuvres entirely: so will someone who has, please explicate 1?
I agree that some parts cannot be skipped (e.g. those integral for the plot), but other parts can, particularly if you are skipping on, and your reading is guided by, the advice of scholars or teachers who have diagnosed which parts are less crucial?