The number of titles in the series eventually came to a total of 14 in English, due to the combination of some paired Dutch volumes into a single volume in English. Among key works were "The Person of Christ", "The Work of Christ", two volumes on "Sin", a volume on "The Providence of God" (which refers to Herman Dooyeweerd's philosophy), "General Revelation" (again refers to Dooyeweerd), and "The Image of God" (which especially made the growing movement of philosophers, scientists, and theologians whose thinking was akin to the ideas of Vollenhoven and Dooyeweerd much more comfortable than they had been under Hepp).