The Congregation for Divine Worship and the Sacraments, headed by Cardinal Sarah, had announced in early March Pope Francis' decision to add the feast to the church's calendar as an "obligatory memorial."

The Monday after Pentecost is May 21 this year. 

Although there are a few specific cases in which the rector of a church or pastor of a parish could choose to celebrate a different Mass that day, Cardinal Sarah said in a note released March 27 that "all else being equal, the obligatory memorial of the Blessed Virgin Mary, Mother of the Church is to be preferred."

In addition, he said, the list of Mass readings published with the Pope's decree "are to be held as proper because they illuminate the mystery of spiritual motherhood."

The Vatican gave two options for the first reading: Genesis 3:9-15, 20, which recounts God questioning Adam and Eve in the garden after they had eaten the forbidden fruit; and Acts 1:12-14, which tells of the disciples gathering in the Upper Room with Mary after the Resurrection. The Gospel reading is John 19:25-34, which recounts Jesus telling his beloved disciple to take Mary into his home as his mother.

In cases where a local or national church calendar has another saint or blessed on the calendar May 21, Cardinal Sarah said, "following the liturgical tradition of pre-eminence amongst persons, the memorial of the Blessed Virgin Mary is to prevail."