Complex sentence: This book expands on the doctrine already begun in Guénon's earlier book "The Symbolism of the Cross", putting aside the geometrical approach developed in that book in order "to bring out the full range of this altogether fundamental theory".
Split into simpler sentences: This book expands on the doctrine whose cornerstones were laid in Guénon's earlier book "The Symbolism of the Cross". Guénon now leaves behind the geometrical approach developed in the earlier book, in order "to bring out the full range of this altogether fundamental theory".