The encyclical on devotion to the Sacred Heart of Jesus, given for the centenary of the extension of the feast to the universal Church by Pius IX. Against the suggestion that the devotion is a sentimental accretion, Pius XII shows its foundations in Scripture, from the covenant love of God in the Old Testament to the pierced side of the Crucified in Saint John, and in the Fathers and the Church's doctors. He explains what is honoured in the Heart of the Incarnate Word: a threefold love — the divine love he shares with the Father and the Spirit, the spiritual love of his human will, and the sensible love of his human affections — all resting on the hypostatic union, so that worship offered to his Heart is worship offered to the Person of the Word made flesh. The encyclical concludes with the practices of consecration and reparation and with the Heart of Jesus as the school of charity for the whole Church.