Faustina was born Helena Kowalska in a small village west of Lodz, Poland on 25 August 1905. She was the third of ten children. When she was almost twenty, she entered the Congregation of the Sisters of Our Lady of Mercy, whose members devote themselves to the care and education of troubled young women. The following year she received her religious habit and was given the name Sister Maria Faustina, to which she added, “of the Most Blessed Sacrament”, as was permitted by her congregation’s custom. In the 1930s, Sister Faustina received from the Lord a message of mercy that she was told to spread throughout the world. She was asked to become the apostle and secretary of God’s mercy, a model of how to be merciful to others, and an instrument for reemphasising God’s plan of mercy for the world. It was not a glamorous prospect.
Her entire life, in imitation of Christ’s, was to be a sacrifice – a life lived for others. At the Divine Lord’s request, she willingly offered her personal sufferings in union with Him to atone for the sins of others; in her daily life she was to become a doer of mercy, bringing joy and peace to others, and by writing about God’s mercy, she was to encourage others to trust in Him and thus prepare the world for His coming again. Her special devotion to Mary Immaculate and to the sacraments of Eucharist and Reconciliation gave her the strength to bear all her sufferings as an offering to God on behalf of the Church and those in special need, especially great sinners and the dying.
She wrote and suffered in secret, with only her spiritual director and some of her superiors aware that anything special was taking place in her life. After her death from tuberculosis in 1938, even her closest associates were amazed as they began to discover what great sufferings and deep mystical experiences had been given to this Sister of theirs, who had always been so cheerful and humble. She had taken deeply into her heart, God’s gospel command to “be merciful even as your heavenly Father is merciful” as well as her confessor’s directive that she should act in such a way that everyone who came in contact with her would go away joyful. The message of mercy that Sister Faustina received is now being spread throughout the world; her diary, Divine Mercy in my Soul, has become the handbook for devotion to the Divine Mercy. – Catholic Online