Complex sentence: He was a connoisseur of the fauna and flora of Castile and was passionate about hunting and the countryside, themes which permeated his writing from the perspective of a city-dweller who had not lost touch with the rural world.
Split into simpler sentences: He was a connoisseur of the flora and fauna of Castile and was passionate about hunting and the countryside. Therefore, these were common themes in his writing, and he often wrote from the perspective of a city-dweller who had not lost touch with the rural world.