The Diary of St. Faustina is the second most important book in the world, after the Bible. It is a record of the inspiring life of St. Faustina, as she experienced the profound supernatural events that shaped her entire life. It reveals the supremely holy and wise personality of the author, not so much in what she said about herself, but in her honest reaction to the ordinary and divine moments of her everyday life. But the true purpose of the Diary was to document the instructions of Jesus as to how He desired the new devotion to His Divine Mercy to be formed. It is this point that makes it the second most important book in the world, because it contains the actual words of Jesus spoken to St. Faustina regarding His Mercy and the new devotion to His Divine Mercy, which He willed to be established in His Church.
One of the first points to note regarding the Diary of St. Faustina is that she was instructed by Jesus and her spiritual directors, Fr. Sopocko and Fr. Andrasz, to write the events of her life in her diary. She records in her diary, that if she had not been instructed to do so, both by Jesus, but more importantly, by her spiritual directors, she would have not done it. In many respects, St. Faustina always sought silence and hugely limited the amount of talking she engaged in and even objected to the writing of unnecessary personal letters, so write a diary of this nature would have been totally against her natural inclinations.
The reason the instructions of her spiritual directors were more important to her than the instructions of Jesus was because the profound supernatural events in her life, such as inner-locutions, divine inspirations and visions, caused St. Faustina tremendous suffering as she often, understandably, doubted if she should trust these supernatural occurrences. At one point, she refused to fulfil a request of Jesus, because her spiritual director would not grant her permission to carry out His instructions. Of course this was completely acceptable to Jesus as He had instructed her on several occasions to be obedient to her spiritual director.
We also know that the contents of the diary and the supernatural events in her life caused her tremendous personal anguish, because one day she decided to burn her diaries. After she informed Fr. Sopocko of what she had done, he demanded that she re-write the entire document from memory, which she duly did. This is why, between 1927-1934, we have large gaps in time where we have no record of her daily life.
It was only after 1934 did she really begin to take seriously the importance of writing the events of her life. But from 1934 until her death in 1938, she dedicated all of her spare time to writing the words, advice and instructions of Jesus regarding the His new devotion, as well as her own spiritual insights and councils. While she was alive, she was adamant that nobody other then her spiritual directors and her religious superiors should read or even know about her diaries. This is why there are many unfinished sentences and paragraphs in the Diary because St. Faustina would close her diaries, if someone came to her room.
She was aware that one day her diaries would be printed but only after she had died. On one occasion, Jesus granted her a vision of how her diary would be discussed in the Vatican in the presence of the Pope and other priests and how Jesus would inspire them to understand the importance of the diary. Jesus clearly indicates that He wished the Diaries to be printed as He often instructed her to write His messages for the consolation of future generations of souls. She records in her diary that on several occasions the devil appeared to her and tried to discourage her from writing the diaries. She wrote that the devil was aware that the diaries would bring countless souls back to God.
Jesus constantly refers to St. Faustina as the ‘secretary’ or ‘administrator’ of His Mercy. It is clear that He greatly desired that she write as much as possible about His Mercy so that every soul would have access to His words and could know about the limitless bounds of His Mercy. On several occasions, He told St. Faustina that He felt that she had not written enough about His Mercy. On thirty-two separate occasions, Jesus gave St. Faustina explicit instructions to write a message for Him, which were messages for all mankind. Some of these messages were warnings that the Justice of God is a reality and that Judgement day was near, but the main abiding theme of His direct messages is that His Mercy, Goodness and Love would refuse no-one, if they turn with trust to His Mercy and seek forgiveness for their sins. He also gave her explicit instructions regarding the various important elements of the devotion such as the Feast of Mercy, the Chaplet, the Novena and the Proclamation of His Mercy. He also made direct promises to all souls in these messages.
It may seem obvious, but probably the most important point to understand about the diary is that it is an actual record of Jesus’ words to St. Faustina. There have been many saints such as Padre Pio, St. Leopold Mandic, St. John Vianney and many others who have had the extraordinary gifts of the Holy Spirit like reading souls and making prophecies, and to whom Jesus appeared and guided them. Some, like St. Catherine of Sienna and St. Theresa of Avila, had extraordinary mystical insights into the nature of God and subsequently wrote breath-taking books on the Divine Mystery. Many of the famous saints had tremendous gifts of healing, like St. Anthony, but the only other saint who had an experience similar to St. Faustina was St. Margaret Mary Alacoque, to whom Jesus spoke to her and gave her instructions about a new devotion to His love which became known as the Sacred Heart Devotion. But even in the Sacred Heart Devotion, Jesus did not instruct her to directly write down His words and instructions. In fact, He requested that a priest, Fr. Jean Croiset, be the person to write the book, which would become the main text for the Sacred Heart Devotion. It was only St. Faustina to whom Jesus gave explicit instructions to write His words regarding the new devotion He wished to establish in the world. This is a further reason why the Diary of St. Faustina is so special. It is because is is absolutely unique in the history of the Catholic Church.