Catholics and Protestants learning from each other "is just an inherently important subject," Kreeft said, noting that when he undertook the project he did not even realize the timing of the book's release would coincide with the year of Protestantism's 500th birthday.
Source: Brandon Showalter - "God Is Moving to Unite Catholics and Protestants as Culture Crumbles, Says Peter Kreeft (Interview)", Christian Post, 31 May 2017, http://www.christianpost.com/news/god-moving-unite-catholics-protestants-culture-crumbles-peter-kreeft-185719/