Which David Spangler book helped spread New Age ideas after 1976?

The book that helped spread New Age ideas after 1976 is Revelation: The Birth of a New Age, written by David Spangler.

Following his time at the Findhorn Foundation, Spangler returned to the United States in the mid-1970s and became a primary architect of the New Age movement. Unlike earlier perspectives that viewed the arrival of a new era as independent of human intervention, Spangler’s work emphasized that individuals must actively use emerging spiritual energies to manifest the New Age. This publication marked the beginning of a series of popular books that helped attract leaders from various occult and metaphysical organizations to the movement.1