A Christian Mannes Bileeve is a little-known Middle English commentary on the Apostles’ Creed that was read by women religious to learn ecclesiastical doctrine. It presents, in a unique way, the figure of the thinking heart to reconcile the gendered binaries of Latin and vernacular, pastoral and devotional, prose and poetry, intellect and affect. Rather than portray Christ in the excessively erotic context usually associated with affective spirituality, A Christian Mannes Bileeve stages a dialogue of voices that teaches how to “think with the heart.” This new understanding of affective piety does not position “heart knowledge” (sapientia) and “head knowledge” (scientia) as mutually exclusive. Instead, A Christian Mannes Bileeve fuses reason (“skil”) with affect (“kyndenesse”), generating a reasonable love borne from gratitude for God that arises from knowing the Apostles’ Creed. The work thus offers a new way of conceiving both women’s affective piety and the relationship between vernacular and clerical theology.