Complex sentence: Malo devoted himself to preaching and in due course became Bishop of Aleth (Saint-Servan) He was succeeded by Saint Gurval who had a church built in honour of his predecessor.
Split into simpler sentences: Malo devoted himself to preaching and in due course became Bishop of Aleth (Saint-Servan). Malo or Saint Malo was succeeded by Saint Gurval who had a church built in honour of his predecessor.