Sister Faustyna described the aim of writing the Diary. By this writing she wanted to fulfil distinct recommending the Lord Jesus and the imperative of confessors both Rev. M Sopoćko as well as O.J. Andrasza T.J. She also revealed, that she wants through this Diary to let people get to know the goodness and the divine grace. She also repeatedly marked, that she wrote it for distinct recommending Superiors what for her confirming the Will of God. The diary in her understanding wasn't supposed to be assigned to read for the wider community, and every time never in her lifetime. Marian Sopoćko is clarifying the aim of writing the Diary still in his letters in the different way. He is emphasizing that the wealth of spiritual experiences of Sister Faustyna was too large so that it is possible to discuss these things in the confessional, without reprimanding the third party. Anyway as the professor he had no time for that kind of long confessions. So he told her to make a list of what she thinks is the will of God and to give it him to seeing through.
The Sister Faustyna wrote down her experiences and special graces systematically. Mainly concentrated on matters of the inner life and her contact with God. Lot of place she devoted to cautions, inspirations and God's orders. Exceptionally sometimes she mentioned certain external facts. On some pages she wrote down reflections and conclusions from meditation or the conference.
And even sometimes directly she wrote down content of heard priestly cautions. On many pages we are finding the poetry, in which she is trying to say its emotions towards God. Poems have character of personal declarations of love and longing for God. In them mainly she expresses love and desire of the full unification with the Creato. She writes without the plan, besides these accents she mentions about the environment in which she lives, about the work and the condition of their health.
The Sister Faustyna started writing the Diary in 1934. The first poem and the note have a the date: 28 July 193. We know from Priest Sopoćko that the Faustyna burnt the certain part of the Diary. Notified about it, told her as the penance to reconstruct destroyed content from the memory and at the same time systematically to register her experiences. It caused complicating the sequence of facts in the serious part of notes of Faustyna. Conscious anyway of it, she printed dates of events sometimes, she wrote about different matters without dates using with epithet - at one point. As a result of it it happened a few of repeating the same fact or surviving. The entire text of the manuscript is contained in six booklets. The manuscript in principle has no damage. There is only one side shaken out (what was marked by the text), by the unknown perpetrator.
Faustyna has very often intertwined descriptions of facts with prayers. Into her own sentences she weaved words of the Lord Jesus in she finished the started story with his words. The lack of the punctuation caused vagueness as a result of it in the text. She has often done this way, she started the description of the thing or matters and she finished it with prayer return to God, or with act of the admiration in view of the God's acting. Particularly a second part of the Diary where facts taken down and experiences pointing a lot of accents of the God's presence. In the manuscript of the Diary we find the row of words needlessly repeated. It permits to suppose she had the ban on crossing what she wrote off. Just therefore most probably left both repeated as well as incorrect or unnecessary words. The state of the manuscript lets also suppose, she didn't read what she had written because then she would certainly finish writing, e.g. in some word a letter being missing.
In manuscript we are find the large sequence of underlines of words and sentences. It was done because of recommendation of Priest Sopoćko which several times told her in this way to mark what the Lord Jesus recommended her.
Booklets of the Diary Sister Faustyna had always near her. She only sometimes gave them for the inspection to Priest Sopoćko, and then Andraszowi T.J Fr. After her death the manuscript stayed in the Congregation. As a matter of fact he was closely guarded, the whole of the Congregation didn't know about its being. When the Andrasz Fr wrote about live of Sister Faustyna, then in the confidence a Diary was made available to him, anyway as for the confessor which had everyfull right to it. For the first time the Diary was copied on the recommendation of General Mother Michaela Moraczewska, by Sister Ksawera Olszamowska. This wasunfortunately inaccurately and not_scientifically. Because this sister has added and missed certain small change of words, changed epithets, and even omitted certain texts. From this text was made more copies as well as it was translated into Italian what worse this text received authorizing and certifying by Curia Krakowska.
With respect to the original copies contain missing entire pages, missing entire sentences, and huge amount of changed words, replaced different, of skipped or added words. The amount of demonstrated mistakes is gaining many sides of the heavy typescript. Nothing so strange, that previous texts met with reservations and the disbelief.
The most worst thing is however a fact of the entire row of stylish vagueness which stayed without the amendment. Because sister Faustyna sister went in the same sentence from own words for quoting words of the Lord Jesus.
At present scientific study of the text is based on original manuscript of Sister Faustyna. Entire critical apparatus, all text notes and indices were worked out by the sister Beata Piekut from gathering the God's Mother of the Mercy together in Poland with the complicity of Sisters which helped at copying texts. As the historian he obliged with his advice and pointers Fr Jerzy Mrówczyński, the Promoter of the Faith of the Information Process.
The text this way prepared and it's study were sent to the Rome on the hand of Postulatora Father General Matters Fr Antoni Mruk T.J., in order to after its verification and under his direction could appear in print. The Diary of Sister Faustyna isn't some set "wonders" and book containing descriptions of extraordinary phenomena. 
Indeed it is valuable and teaching reading. Above all for us it is uncovering the inner life of the God's servant. From cards of the Diary she appears us as the hard man for herself and determined in the work on oneself. We can see how the Faustyna insistently worked and made the most of every opportunity for spiritual making rich herself. We learn from the Diary we know about her problem and spiritual darkness, as well as about her mystical ascents, enlightenments and internal solaces. However the most important this is her an inner strength, coming of course from leaning against God and an undoubted heroism of the confidence in the God's Mercy.
The diary shows for us the infinity of the God's Mercy. It not only teaches about the Saviour, but also encourages for his worship. It points on also different forms of this reverence, and all at the same time it illustrates facts of God's intervention.
The diary still has this value, that it teaches the child's and full of the simplicity relationship to God, that it shows the possibility of having intercourse with God by us for every moment.
It shows living in the God's presence as the grace admittedly, but as the grace possible to attain through prayer for oneself towards God.
However an advantage of the Diary is a caution and an incentive to the intense internal Living. It shows us the necessity of the strenuous and determined work on oneself on the example of the Faustyny Sister. It is also practically teaching loves to neighbours.