Who foreshadowed the development of positive psychology by considering what makes some people healthy minded and others to have a sick soul in his book, the varieties of religious experience?

The answer is William James. He was an American philosopher and psychologist who was also taught as a physician. He is also known as the Father of American psychology. His book (Varieties) includes his edited Gifford Lectures on natural theology, which were delivered at the University of Edinburgh in Scotland in 1901 and 1902. The discourses concerned the nature of religion and the neglect of science in the academic study of religion. Shortly after its publication, Varieties go into the Western canon of psychology and philosophy and has remained in reproduction for over a century.