An encyclical on the human and divine love of the heart of Jesus Christ, published in the 350th anniversary year of the first apparitions to Saint Margaret Mary Alacoque at Paray-le-Monial. Its five chapters treat the importance of the heart in a fragmented age, the gestures and words of Christ's love in the Gospels, the Church's reflection on that love from the Fathers through the mystics and the great devotional tradition, the drinking from the wellspring of the pierced side in acts of reparation and consecration, and finally love that gives itself in mission and communal reparation, so that the devotion is never merely private sentiment.