Devotion to the Sacred Heart of Jesus is founded on orthodox Christology hammered out in the first centuries of the Church. Our Lord's human nature and His divine nature are united in one person - this is called in theology the hypostatic union. Following on from this doctrine, anything we predicate of Christ, either according to his human nature or his divine nature, is predicated of the one person Jesus Christ the Word made flesh. (What theologians call the "communication of idioms") So we can say that God the second person of the Blessed Trinity, was born of the Virgin Mary, suffered, and was sometimes hungry; we can also say that the man Jesus was omnipotent, all-knowing, and infinitely loving. In the devotion to the Sacred Heart, we think especially of the human love of God made man. We can also speak of His emotions of joy and of sorrow that flow from that love. Our Lord was joyful when people responded to Him in faith, and He was sorrowful when people sinned.
