The Divine Mercy was already very close to the spirituality of the Sacred Heart of Jesus. Even St. Margaret Maria Alacoque in her writings spoke about the Merciful Heart of Jesus. St. Faustina Kowalska in the 20th century, especially, spread the devotion to the Divine Mercy.
The Church recognized her through a serious process of beatification and canonization, the holiness of her life. The Church also acknowledged her writings as conforming to the Catholic faith and that it is a healthy devotion. So, it's approved by the Church that she lived a holy life. It was proven, and therefore this devotion is correct. The Church was observing and they proposed this.
Maybe not all people know but, in her writings, she described hell in detail. She wrote in her diary about hell and how souls can be condemned for all eternity. Therefore, she spread the Divine Mercy to save souls from hell. She also insisted on the reality of hell, and she even saw the souls in hell, like the children of Fatima.
And so, we have to do these, to read all the messages or the writings of Sister Faustina, and to invite people to the Divine Mercy. It is an instrument to save souls from hell. We have to stress this: to offer them the possibility to repent because the Divine Mercy and even St. Faustina have said that it always presupposes deep repentance. And only a repentant heart will recognize the beauty of the Divine Mercy. And every day, in every sacrament of confession, we all experience the greatness and beauty of the Divine Mercy towards ourselves.
Dear visitors of Gloria Dei and all who have already written or who will write a personal message to me. I am grateful for your attention, your kindness, for your spiritual support and especially for your sacrifices and prayers for me. God may reward you!