Complex sentence: This is because Lewis' purpose in writing about his life was not primarily for historical purposes, instead, his aim was to identify and describe the events surrounding his accidental discovery and consequental search of the phenomenon he labeled Joy.
Split into simpler sentences: This is because Lewis' purpose in writing about his life was not primarily for historical purposes. Instead, his aim was to identify and describe the events surrounding his accidental discovery and consequental search of the phenomenon he labeled Joy.