The correct option is D Because he thinks that the philosophical errors committed by the abstruse philosopher will come into light only to the posterity that has the advantage of hindsight in regards to how the thought has played out in practice.
Option A suggests that the posterity will be inherently more just than the previous generation. This is nowhere stated nor can be inferred from the passage. Also, ‘equitable’ here is not in the sense of justness but more in the sense of being knowledgeable. Options B and C may look plausible but on close observation of the last paragraph: ‘that abstract reasoners seem hitherto to have enjoyed only a momentary reputation, from the caprice or ignorance of their own age, ‘ it is apparent that people of the abstruse philosopher’s time may have regarded him with positivity due to the prevalent ignorance or caprice. However it does not say anything about why the next generation should be more equitable. Option D suggests that the posterity will have the advantage of getting to know the philosopher’s thoughts both in theory and in practice, compare them and judge him for his philosophical accuracy. In this regard, they will be more knowledgeable or equitable.