One of many books written by Mary Baker Eddy, the founder of Christian Science. The book is the complete Christian Science textbook, and teaches how healing can be performed, and that sickness is only mortal error. The book contains the main concept of Christian Science, which is best stated by quoting the actual text. What follows is on page 468 of S&H in a chapter entitled Recapitulation:

Question - What is the scientific statement of being?
Answer - There is no life, truth, intelligence, nor substance in matter. All is infinite Mind and its infinite manifestation, for God is All-in-all. Spirit is immortal Truth, matter is mortal error. Spirit is the real and eternal; matter is the unreal and temporal. Spirit is God, and man is His image and likeness. Therefor man is not material; he is spiritual.

The words Mind, Spirit, All, and Truth are capitalized because they are all different names for God.