Synthesized answer
The central thesis of Carl Gustav Jung's *Modern Man in Search of a Soul* is a study about man and his spiritual search [1]. The work explores the inner life and spiritual needs of contemporary individuals.
The passages provided indicate that the book delves into man's spiritual quest. However, the specific arguments or central claims that articulate the core thesis are not detailed in the given text. Therefore, while the subject matter is identified as man's spiritual search, the precise thesis remains unstated.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: Modern man in search of a soul by Carl Gustav Jung Description: study about man and his spiritueal search