The dialectical pattern of regarding Martin Luther's thought goes on. Protestant church historians have traditionally seen the Reformation as the end of the medieval Catholic paradigm and the beginning of modernity. In the mid- to later twentieth century, Heiko Oberman pointed out the Wittenberg divine's indebtedness to late medieval theologians and in the process diminished the level of this thinker's originality. The year 1500 ought, he repeated, never to be regarded as the end of one era and the beginning of another. Rex unselfconsciously returns to the prior pattern: Luther's core precepts were entirely novel. Between 1518 and 1525 (after which, Rex says, his ideas stopped developing), he broke decisively with prior norms of belief. He affirmed the Christian's absolute certainty of saving grace, a ‘dramatic innovation’ (p. 142). The doctrine of justification by faith, which Rex dates to 1518, did away with the need to worry and strive by diverse means to find favour with God. Good works became sins. He abolished every prior source of religious truth except Scripture alone, thereby dismissing his opponents’ resort to popes and ancient Fathers and councils. Indeed, he denominated the pope as the AntiChrist. He introduced the concept of the ‘invisible Church’ of the faithful. He defined the mass as a testament and not a sacrifice or a covenant. He placed the individual conscience at the centre of spiritual life even as he rejected the arguments that his rival exercisers of conscience, men like Andreas Bodenstein von Carlstadt and Ulrich Zwingli, advanced. Indeed, the writer ascribes an ‘essential individualism’ to Luther's entire theology (p. 146). Rex does not quite ignore either Luther's own temperament (he raged; he was a ‘monstrous egotist’, p. 3) or the fact that, in the end, he cooperated with his princes. Yet much of the concrete world around the Reformer does not appear. The Turks are not mentioned once. Reading this book was a rewarding experience. The author demonstrates a broad acquaintance with the culture of the times. It remains to be seen how Rex's interpretation fits into the veritable outpouring of new works on the Reformer during 2017. I warrant it will be seen as conservative.