Ecclesia de Eucharistia §27

²⁷ The Catechism of the Catholic Church , in explaining how the Church is apostolic – founded on the Apostles – sees three meanings in this expression. First, “she was and remains built on 'the foundation of the Apostles' ( Eph 2:20), the witnesses chosen and sent on mission by Christ himself”. The Eucharist too has its foundation in the Apostles, not in the sense that it did not originate in Christ himself, but because it was entrusted by Jesus to the Apostles and has been handed down to us by them and by their successors. It is in continuity with the practice of the Apostles, in obedience to the Lord's command, that the Church has celebrated the Eucharist down the centuries. The second sense in which the Church is apostolic, as the Catechism points out, is that “with the help of the Spirit dwelling in her, the Church keeps and hands on the teaching, the 'good deposit', the salutary words she has heard from the Apostles”. Here too the Eucharist is apostolic, for it is celebrated in conformity with the faith of the Apostles. At various times in the two-thousand-year history of the People of the New Covenant, the Church's Magisterium has more precisely defined her teaching on the Eucharist, including its proper terminology, precisely in order to safeguard the apostolic faith with regard to this sublime mystery. This faith remains unchanged and it is essential for the Church that it remain unchanged.