Napier had an interest in the Book of Revelation, from his student days at St Salvator's College, St Andrews. Under the influence of the sermons of Christopher Goodman, he developed a strongly anti-papal reading.[3] He further used the Book of Revelation for chronography, to predict the Apocalypse, in A Plaine Discovery of the Whole Revelation of St. John (1593), which he regarded as his most important work; he also applied the Sibylline Oracles, to calculate the date of the end of the world.[5] Napier believed that would occur in 1688 or 1700. He dated the seventh trumpet to 1541.