The Title Page of Calvin's Institutes Calvin's Institutes of the Christian Religion (Institutio Christianae religionis) is perhaps the single most important work on Protestant theology. Published first in Latin in 1536, when Calvin was only twenty-five, it offers a systematic introduction to his thought and an introductory textbook to the beliefs of the Reformed churches. Rejecting many of the doctrines and sacraments of the Catholic Church, it argues for sola fide, justification or salvation by faith alone, and asserts Calvin's historically important views on predestination and election to salvation.