There are many saints who in their writings expressed their deep understanding and appreciation for for The Divine Mercy.
St. Ambrose (339-397) - Prayer (Preparation for Mass)
"Lord Jesus Christ, I approach your banquet table in fear and trembling, for I am a sinner, and dare not rely on my own worth, but only on your goodness and mercy. I am defiled by many sins in body and soul, and by my unguarded thoughts and words.
Gracious God of majesty and awe, I seek your protection, I look for your healing.
Gracious God of majesty and awe, I seek your protection, I look for your healing. Poor troubled sinner that I am, I appeal to you, the fountain of all mercy. I cannot bear your judgment, but I trust in your salvation. Lord, I show my wounds to you, and uncover my shame before you. I know my sins are many and great, and they fill me with fear, but I hope in your mercies, for they cannot be numbered.
Lord Jesus Christ, eternal king, God and man, crucified for mankind, look upon me with mercy and hear my prayer, for I trust in you. Have mercy on me, full of sorrow and sin, for the depth of your compassion never ends.
Praise to you, saving sacrifice, offered on the wood of the cross for me and for all mankind. Praise to the noble and precious blood, flowing from the wounds of my crucified Lord Jesus Christ and washing away the sins of the whole world. Remember, Lord, your creature, whom you have redeemed with your blood; I repent my sins, and I long to put right what I have done.
Merciful Father, take away all my offenses and sins; purify me in body and soul, and make me worthy to taste the holy of holies. May your Body and Blood, which I intend to receive, although I am unworthy, be for me the remission of my sins, the washing away of my guilt, the end of my evil thoughts, and the rebirth of my better instincts. May it incite me to do the works pleasing to you and profitable to my health in body and soul, and be a firm defense against the wiles of my enemies. Amen."
St. Catherine of Siena (1347-1380) - Prayer to Divine Mercy
"0 eternal Mercy, you who cover over your creatures' faults! By your mercy we were created. And by your mercy we were created anew in your Son’s blood. It is your mercy that preserves us. Your mercy made your Son play death against life and life against death on the wood of the cross. In him life confounded the death that is our sin.
I see your mercy pressing you to give us even more when you leave yourself with us as food to strengthen our weakness, so that we forgetful fools should be reminded forever of your goodness.
"Who was conquered? Death! And how? By your mercy! You temper your justice with mercy. In mercy you cleansed us in the blood; in mercy you kept company with your creatures.
"O mad lover! It was not enough for you to take on our humanity, you had to die as well! Nor was death enough: you descended to the depths to summon our holy ancestors and fulfill your truth and mercy in them. I see your mercy pressing you to give us even more when you leave yourself with us as food to strengthen our weakness, so that we forgetful fools should be reminded forever of your goodness.
"And what has done this? Your mercy. O mercy! My heart is engulfed with the thought of you! For wherever I turn my thoughts, I find nothing but mercy!" (Dialogue 30).
St. Therese of Lisieux, or of the Child Jesus, or the Little Flower (1873-1897)
Her fundamental vision of God was that God is towards us not only Love but merciful Love. She had spoken and written so feelingly about the merciful love of Him whose Heart is an ocean of mercy.
What sweet joy to think that the Lord is just, that He takes into account our weakness and knows so fully well the frailty of our nature. What then need I fear?
"After so many graces which I have received, may I not sing with the Psalmist: "The Lord is good; His mercy endures for ever." It seems to me that if everyone received such graces, no one would dread God but all would love Him with an unbounded love. Through sheer love, without any thought of fear, no one would ever willfully commit the least fault. But then I realize that all souls cannot be alike; they must differ so as to honor the different perfections of God.
"To me He has given His Infinite Mercy, and it is in this resplendent mirror that I gaze upon all His other attributes. There all appear radiant with love; even justice, perhaps more than the others, seems to me clothed with love...
"What sweet joy to think that the Lord is just, that He takes into account our weakness and knows so fully well the frailty of our nature. What then need I fear? Surely the good God of infinite justice who deigns to pardon with such mercy the sins of the prodigal son, will also be just towards me who am always with Him… I have only to look at the holy Gospel; I breathe the fragrance of the life of Jesus and I know which way to go... twill follow, the example of Mary Magdalene, her astonishing or rather her loving audacity which so delighted the Heart of Jesus.
"It is not because I have been preserved from mortal sin that I go to God with confidence and love. Even if I had on my conscience all the crimes that one could commit, I am sure I would lose nothing of my confidence; I would throw myself, my heart broken with sorrow, into the arms of my Savior. I know how much He loves the prodigal son; I have heard His words to Mary Magdalene, to the woman taken in adultery, to the Samaritan woman. No, there is no one who could frighten me, for I know too well what to believe about His mercy, about His love. I know that in the twinkling of an eye, all those thousands of sins would be consumed as a drop of water cast into a blazing fire." (Last pages of manuscript C).
These were the last words which Theresa wrote before her death; owing to weakness she could not write any more, but said to Mother Agnes, her eldest sister, to take down the story of the sinful woman who died of love; then she dictated to her, word for word, the following lines:
"In the "Lives of the Fathers of the Desert," we are told that one of them converted a public sinner whose evil doings had been the scandal of a whole country. Touched by grace, the sinful woman followed the saint into the desert to perform there rigorous penance, but on the first night of her journey, even before she had reached the place of her retirement, the vehemence of her loving sorrow broke the ties that bound her to earth, and the holy man saw her soul, that very moment, borne by angels into the arms of God. This is a striking illustration of what I want to say, but these things cannot be expressed in words." (Derniers entretiens, p. 70)