Beginning with the Upper Room and Holy Thursday, the celebration of the Eucharist has a long history…In the course of this history, the secondary elements have undergone certain changes, but there has been no change in the essence of the “Mysterium” instituted by the Redeemer of the world at the Last Supper. The Second Vatican Council too brought alterations, as a result of which the present liturgy of the Mass is different in some ways from the one known before the Council.

–St John Paul II (Dominae Cenae, 1980)