§1356
Sacraments › … › V. The Sacramental Sacrifice Thanksgiving, Memorial, Presence
If from the beginning Christians have celebrated the Eucharist and in a form whose substance has not changed despite the great diversity of times and liturgies, it is because we know ourselves to be bound by the command the Lord gave on the eve of his Passion: "Do this in remembrance of me."
Source: Catechism of the Catholic Church (Vatican.va)