Jesus appeared to Saint Faustina and revealed His Divine Mercy for the world.

He chose Sr. Mary Faustina as the Apostle and "Secretary" of His Mercy, so that she could tell the world about His great message. In the Old Covenant — He said to her —I sent prophets wielding thunderbolts 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).