The mystery of mercy is closely linked to the mystery of the Sacred Heart of Jesus, it is its continuation and development. This is reflected in the iconography. The tradition of depicting the Sacred Heart of Jesus was most widespread in the first half of the twentieth century, when his cult reached the peak of popularity.
On July 1, 1934, when Kazimierowski was finishing painting the image of Merciful Jesus in his studio, the whole of Lithuania was solemnly entrusted to the care of the Sacred Heart of Jesus. In the same year, the Church celebrated the 1900th anniversary of the crucifixion of Jesus – the Jubilee of the Heart of Jesus.
Already after the end of the jubilee, on the Guiding Sunday of 1935, the image of Merciful Jesus was hung for the first time in the Gate of Dawn.
In addition, the painting itself was painted in the painting studio on Rossa Street, next to the Church of the Sacred Heart of Jesus and the convent of the Visitation Sisters. Marguerite Mary Alacoque, a precursor of the cult of the Heart of Jesus who lived in the seventeenth century, was also a sister of this congregation in France. In her diary, Faustina repeatedly refers to the Heart of Jesus as the source of mercy: “These two rays came out of the bowels of My mercy when My dying heart was opened on the cross with a lance” (Diary, 299). Of the rays, the Savior said, “they signify blood and water. The pale ray signifies the water that justifies souls; The red ray signifies the blood, which is the life of souls […] These two rays reveal the soul to the wrath of My Father. Happy is he who lives in their shadow, because the just hand of God will not reach him (Diary, 299). For Blessed Father Michael Sopocko, who sought to deeply understand the message of Sister Faustina’s apparition and to evaluate the authenticity of the visions, it was very important to find their confirmation in Sacred Scripture and in the tradition of the Fathers of the Church.
As early as the fourth century, John Chrysostom linked the streams flowing from the heart of Jesus to the sacraments: “Water and blood were symbols of baptism and mysteries. From both of them the Church was born, through this washing of rebirth and renewal in the Holy Spirit, through Baptism and mystery.”
Source: Dievo Gailestingumo Šventovė | The meaning of the image of Merciful Jesus (gailestingumas.lt)