The Sacred Heart of Jesus and the Immaculate Heart of Mary have been intimately related to one another ever since the moment of Incarnation. Most parents know, especially Mothers, that if there is one thing that connects them to their child, it is the heart. Faithful Christians throughout the Church's history have deductively assimilated the connective reality between the hearts of Jesus and Mary through study of the Gospels, private revelation, and reason. Like all orthodox Christian practices, these devotions flow from Christ's divinity.
The Catholic Encyclopedia presents three foundational aspects for the devotion to the Sacred Heart of Jesus: the historical, the theological, and the scientific:
(a) Historical foundations
In approving the devotion to the Sacred Heart, the Church did not trust to the visions of St. Margaret Mary; she made abstraction of these and examined the worship in itself. Margaret Mary's visions could be false, but the devotion would not, on that account, be any less worthy or solid.
However, the fact is that the devotion was propagated chiefly under the influence of the movement started at Paray-le-Monial; and prior to her beatification, Margaret Mary's visions were most critically examined by the Church, whose judgment in such cases does not involve her infallibility but implies only a human certainty sufficient to warrant consequent speech and action.
(b) Theological foundations
The Heart of Jesus, like all else that belongs to His Person, is worthy of adoration, but this would not be so if It were considered as isolated from this Person and as having no connection with It. But it not thus that the Heart is considered, and, in his Bull "Auctorem fidei", 1794, Pius VI authoritatively vindicated the devotion in this respect against the calumnies of the Jansenists. The worship, although paid to the Heart of Jesus, extends further than the Heart of flesh, being directed to the love of which this Heart is the living and expressive symbol. On this point the devotion requires no justification, as it is to the Person of Jesus that it is directed; but to the Person as inseparable from His Divinity. Jesus, the living apparition of the goodness of God and of His paternal love, Jesus infinitely loving and amiable, studied in the principal manifestations of His love, is the object of the devotion to the Sacred Heart, as indeed He is the object of the Christian religion. The difficulty lies in the union of the heart and love, in the relation which the devotion supposes between the one and the other. Is not this an error long since discarded? If so, it remains to examine whether the devotion, considered in this respect, is well founded.
(c) Philosophical and Scientific foundations
In this respect there has been some uncertainty amongst theologians, not as regards the basis of things, but in the matter of explanations. Sometimes they have spoken as if the heart were the organ of love, but this point has no bearing on the devotion, for which it suffices that the heart be the symbol of love, and that, for the basis of the symbolism, a real connection exist between the heart and the emotions. Now, the symbolism of the heart is a fact and every one feels that in the heart there is a sort of an echo of our sentiments. The physiological study of this resonance may be very interesting, but it is in no wise necessary to the devotion, as its foundation is a fact attested by daily experience, a fact which physiological study confirms and of which it determines the conditions, but which neither supposes this study nor any special acquaintance with its subject.
PRAYER TO THE SACRED HEARTS
O Heart of Jesus pierced for our sins and giving us your Mother on Calvary! O Heart of Mary pierced by sorrow and sharing in the sufferings of your divine Son for our redemption! O sacred union of these Two Hearts! Praised be the God of Love who united them together!
May we unite our hearts and every heart so that all hearts may live in unity in imitation of that sacred unity which exists in these Two Hearts. Triumph, O Sorrowful and Immaculate Heart of Mary! Reign, O Most Sacred Heart of Jesus! – in our hearts, in our homes and families, in the hearts of those who a yet do not know you, and in all nations of the world. Establish in the hearts of all mankind the sovereign triumph and reign of your Two Hearts so that the earth may resound from pole to pole with one cry: Blessed forever be the Most Sacred Heart of Jesus and the Sorrowful and Immaculate Heart of Mary!
Obtain for me a greater purity of heart and a fervent love of the spiritual life. May all my actions be done for the greater glory of God in unions with the divine heart of Jesus and the Immaculate Heart of Mary. Hear and answer our prayers and intentions (mention your petition) according to your most merciful will. Amen.
Most Sacred Heart of Jesus, Have Mercy on us!
Immaculate Heart of Mary, Pray for us!
Most Sacred Heart of Jesus, Your kingdom come!