In 'The Religion of the Heart, ' Campbell provides a critical but sympathetic analysis of the European and British pietistic movements of the seventeenth and eighteenth centuries. Campbell shows that a definitive form of religious life emerged during the period of inter-Christian warfare in the seventeenth century that was characterized by personal affection for God. Campbell explores these religious movements parallel to the rise of Enlightenment thought and examines their importance in relation to our understanding of modern religious movements