Peter Lombard’s major work, the four books of the Sentences, was written in the mid-twelfth century and, as early as the 1160s, the text was glossed and commented on in the schools. There is hardly a theologian of note throughout the rest of the Middle Ages who did not write a commentary on the Sentences. Yet in spite of its importance in Western intellectual history and its capacity to excite generations of students and teachers, the Sentences has received little attention in recent times. Indeed, it has been called “one of the least read of the world’s great books”.

Book 3 closed with a reflection on the relative inadequacy of the Old Law, because what it commanded could not be done well or easily in the absence of grace. While the sacraments of the Old Law were only signs, the sacraments of the Church are also the principal instruments of that grace now freely available to Christians. These sacraments are the main subject of Book 4, taking up forty-two of its fifty Distinctions: Baptism is treated in Distinctions 2–6, confirmation in 7, the Eucharist in 8–13, penance in 14–22, extreme unction in 23, sacred orders in 24 and 25, and marriage in 26–42. The Book concludes with eight Distinctions on the last things – the resurrection of the body, purgation, hell, the last judgement, and eternity.