On October 5, 1938, a young religious by the name Sister Faustina (Helen Kowalska) died in a convent of the Congregation of Sisters of Our Lady of Mercy in Cracow, Poland. She came from a very poor family that had struggled hard on their little farm during the terrible years of WWI. Sister had had only three years of very simple education. Hers were the humblest of tasks in the convent, usually in the kitchen or the vegetable garden, or as a porter.
On February 22, 1931, Our Lord and Savior Jesus Christ appeared to this simple nun, bringing with Him a wonderful message of Mercy for all mankind.
Divine Mercy Devotions: https://www.ewtn.com/catholicism/devotions/divine-mercy-12705