I think OP was saying that knowing Shakespeare is inherently important because it transforms your ability to think. For example, take a case where someone knows how to think, and has read relatively easy children's authors like Enid Blyton. This person would still have learnt to think from writing a a critical analysis of whatever novel they've read.

However their ability to think is still limited to merely the thought processes of an author for children ( Disclaimer: I have no intention of belittling Enid Blyton here).

By just reading Enid Blyton you can't think in terms of metaphors or similes or puns etc. By reading Shakespeare you gain an inherent ability to think in a completely new way. This is also perhaps very similar to what PG says in ANSI Common LISP about LISP's unusual appearance, to quote PG: ' You have to think in a language to write programs in it, and it's hard to want something you can't describe. When I first started writing programs-- in Basic-- I didn't miss recursion, because I didn't know there was such a thing.' Similarly if you didn't know there was such a thing as personification, you wouldn't miss it!