Complex sentence: Bede represented the native British church as wicked and sinful, in order to explain why Britain was conquered by the Anglo-Saxons: he drew on the polemic of Gildas and developed it further in his own works.
Split into simpler sentences: Bede represented the native British church as wicked and sinful. In order to explain why Britain was conquered by the Anglo-Saxons, he drew on the polemic of Gildas and developed it further in his own works.