Sentence:  Firstly, you must not expect too much from this science, for you cannot set contrary brains to rights by any logic. Secondly, you must not think too little of it, by regarding the matter as mere scholastic <WSD>wordmongery</WSD> and useless hairsplitting. 
Meaning of the word marked with <WSD> tags:  Clever writing or speaking, especially that which is superficially impressive but of very little substance.