The paper analyses the work Specchio di croce, written in the vernacular by the preacher Brother Domenico Cavalca around 1330 for a lay public of devoted faithful. Firstly, the catechetic nature of the work is highlighted, showing that it appears as a descriptive summa of Christian doctrine. This is followed by careful focus on what can be seen as the main objective of the work, namely nothing less than a reform of the affections, to be achieved by starting from the image of the Crucifix. Attention then turns to the theological and psychological presuppositions of this affective pedagogy, also identifying the different phases and the constant reference to the Augustinian and Cistercian traditions.