Complex sentence: Nicholas is described not by his valor in battle or honor in the court but instead his many skilled are described at great length, including the fact that he is studying one of the many scholarly arts that were popular at that time.
Split into simpler sentences: Nicholas is described not by his valor in battle or honor in the court. Instead, his many skills are described at great length, including the fact that he is studying one of the many scholarly arts that were popular at that time.