In 1934, Sister Faustina began to write her Diary with Jesus’ revelations to her, in obedience to her spiritual director, Father Michael Sopocko. Sister Faustina’s diary is the principal testimony we have from her, where she recorded in detail the messages that Jesus gave her regarding his inexhaustible mercy to the whole mankind. In it is revealed her profound spiritual life, her struggle to perfection, and God’s predilection toward her. She received the gifts of contemplation, frequent visions of Jesus Christ, apparitions of the Blessed Virgin, Jesus’ revelations, stigmata, the gift of prophecy, readings of human souls, the rare gift of mystical engagement, and marriage….however, she did not give any importance to these as she was very humble.
Saint Maria Faustina accepted the invitation of Jesus as the apostle and “secretary” of His Mercy, so that she could tell the world about his great message of the Mercy of God: "In the Old Covenant", He said to her, "I sent prophets wielding hunderbolts to my people. Today I am sending you with my mercy to the people of the whole world. I do not want to punish aching mankind, but I desire to heal it, pressing it to my merciful Heart"(Diary 1588). "You are the secretary of My mercy. I have chosen you for that office in this life and the next life"(Diary, 1605) (…)to make known to souls the great mercy that I have for them, and to exhort them to trust in the bottomless depth of My mercy” (Diary, 1567). ”Mankind will not have peace until it turns with trust to my Mercy”(Diary, 300).
The mission of Saint Faustina consisted in three main tasks :
1. Reminding the world of the truth of our faith, revealed in the Holy Scripture about the Merciful Love of God towards every human being;
2. Propagating God’s Mercy for the whole world and especially for sinners, through the practice of new forms of devotion to the Divine Mercy, presented by the Lord Jesus such as: the veneration of the Image of the Divine Mercy with the inscription: "Jesus, I trust in you"; the Feast of the Divine Mercy celebrated on the first Sunday after Easter; the Chaplet to the Divine Mercy and the prayer at the Hour of Mercy (3 p.m.). Our Lord Jesus attached great promises to the above forms of devotions, provided one entrusted one's life to God and practised active love of neighbour. Each soul is to put his complete trust in God.
3. Initiating the Apostolic Movement of the Divine Mercy, whose task is to proclaim and entreat God's mercy for the world, and to strive for Christian perfection, following the precepts of Sister Maria Faustina.
Sister Faustina, consumed by tuberculosis and innumerable sufferings which she accepted as a voluntary sacrifice for sinners, died in Krakow at the age of 33 on October 5, 1938. Pope John Paul II beatified Sr. Faustina on April 18, 1993, and canonized her on April 30, 2000. She became the first Saint of the second millennium.
“Saint Faustina, you told us that your mission would continue after your death and that you would not forget us “(Diary, 281, 1582).