Janet O. Hagberg. The Critical Journey : Stages in the Life of Faith. New York, Sheffield Pub Co, 1995.

Stages in the Life of Faith by Janet O. Hagberg and Robert A. Guelich is a book describing six stages of spiritual growth and faith development, focusing on the internal and external changes people experience in their relationship with God. It maps the journey from initial recognition of God through productive service, crises of faith, and eventual mature, loving service.