In the Diary Sister Faustina described her spiritual life, which was exceptionally profound, culminating in union with God in mystical marriage with Jesus. She wrote how deeply she came to know the mystery of the Divine Mercy and how she contemplated it in her daily life. She also wrote about her struggle against the weakness of human nature and the difficulties she came up against in carrying out her prophetic mission. Above all, the Diary contains the message of God’s merciful love for humankind, which Sister Faustina was required to pass on to the Church and the world. This makes her Diary a special work, as the Holy Father, Pope John Paul II, said, “the gospel of mercy written from the 20th-century perspective.”