It was in February 1931, in the Church in Płock, that the Lord Jesus first spoke to Sister Faustina about the desire to establish this feast, and He returned to this issue in several revelations. No wonder that at first only Sister Faustina celebrated this feast according to the wishes and recommendations of Jesus (cf. Diary 280, 89, 420, 1073-1074), seeing that her role in this task consisted not only in informing her Vilnius spiritual guide about Jesus’ words, but also in supporting his efforts with her prayers and suffering. Father Michał Sopoćko wrote theological articles and dissertations, in which he sought to justify the need for this feast in the liturgical calendar of the Church and to show the benefits it would bring for pastoral care. He sought support for this idea among theologians and bishops, and even went to Rome to submit the matter personally to the Congregation.
The 1959 Notification of the Holy See, which prohibited spreading devotion to the Divine Mercy in the form given by Sister Faustina, hampered efforts to establish the feast, but did not disturb the work of theologians, among whom were both zealous advocates of its institution and its strong opponents. After the cancellation of the Notification by the Holy See in 1978, and a complete analysis of Sister Faustina’s writings conducted by Father Ignacy Różycki, and following the publication of Pope John Paul II’s encyclical, Dives in Misericordia, Cardinal Franciszek Macharski, Archbishop of Kraków, in his 1985 Lenten letter, established the Feast of The Divine Mercy in his diocese. In subsequent years, bishops of other dioceses followed the Archbishop of Kraków’s lead. In 1995, the Holy Father John Paul II, acceding to the request of the Primate, Cardinal Józef Glemp, and of the Polish Episcopal Conference, agreed to introduce this feast to the liturgical calendar of the Church in all the dioceses in Poland. On the canonization day of Sister Faustina, on the first Sunday after Easter, 30 April 2000 – the Holy Father established the Feast of The Divine Mercy for the whole Church. In the document of the Congregation for Divine Worship and the Discipline of the Sacraments, we read:“Pope John Paul II has graciously commanded to add to the Roman Missal the term ‘Divine Mercy Sunday’ after the title ‘Second Sunday after Easter,’ and ordered that the texts must always be used as given in the Missal for this Sunday’s liturgy and in the Liturgy of the Hours of the Roman Rite.” The Congregation announced these provisions of the Holy Father on 5 May 2000 stating that they should be executed “regardless of any regulations to the contrary.”