Our Lord’s love for us is both divine and human, for He possesses both a divine and a human nature and will. Hence we may regard the Savior’s Most Sacred Heart as the symbol of His threefold love for us-divine love, spiritual human love and sensitive human love. Yet this Heart is not a formal image or sign of His love, but only its trace. For-as Pius XII says in his encyclical “Hauriets aquas” of May 15, 1956-no created image could represent the reality of this infinite, merciful love.
In the devotion to the Sacred Heart of Jesus, then, we honor above all Our Lord’s human love for mankind, and also His divine love for us, which, being love for the wretched, is really Divine Mercy. So, in this devotion, it is only the faint outline of God’s Mercy that we honor, for we see it there only, as it were, in bud. In the devotion to the Divine Mercy, a more appropriate material object is the blood and water which flowed from the Savior’s side on the cross. These are a symbol of the Church, brought forth from the side of the dead Savior on the cross, This blood and water flow ceaselessly in the Church as graces cleansing the soul (in the sacraments of baptism and penance), and as graces giving life (in the Sacrament of the Altar). Their Author is the Holy Spirit, whom the Saviour gave to the Apostles. The true object of this devotion-its motive – is the infinite Mercy of God the Father, Son and Holy Spirit towards fallen man. This is indeed the love of God for mankind, but only in a wider sense, for it is not the love which delights in perfections, but a compassionate love aroused by the misery in which man found himself after his sin.
We see from the foregoing that devotion to the Divine Mercy is the logical consequence of devotion to the Sacred Heart of Jesus, where it existed only in embryo. It now makes its appearance separately and is not identified with the other devotion, for its material and formal object is not the same. Its aim, too, is completely different. It is related to all Three Persons of the Blessed Trinity, and not-as in the case of devotion to the Sacred Heart-to the Second Person alone; it is, moreover, better suited to the spiritual condition of present-day man, who stands in such need of trust in God. “Jesus, I trust Thee!”, and, through Thee, I trust the Father and the Holy Spirit. (Vol. II, p. 204-205)
Devotion to the Mercy of God – that mercy which He gives us in the Sacrament of Penance-is one of those devotions which befit all souls alike. For the aim of this devotion is to praise the Most Merciful Saviour, not in any one particular state or mystery, but in His universal Mercy, in which all mysteries are revealed at their most profound. And although this is obviously a separate devotion, it contains something which is of general application. This is expressed in the ejaculatory prayer: “Jesus, I trust in Thee”, sinfulness, and, at the same time, arouses the virtue of trust – that virtue on which our justification is founded. (Vol. II, p. 263)