“The parts of the Mass
According to the Gospel narrative, ‘whilst they were at supper, Jesus took bread, and blessed, and broke: and gave to His disciples, and said: Take ye, and eat. This is My body. And taking the chalice, He gave thanks, and gave it to them, saying: Drink ye all of this. For this is my blood of the New Testament which shall be shed for many unto the remission of sins’ (St. Matthew, xxvi. 26-28).
The words and actions of Our Lord constitute the very essence of the Mass; but around them the Church has built up, during the centuries, a most inspiring liturgy that is now enshrined in the Missal. The Mass consists of varying and unwearying parts. The part that does not vary is known as the Ordinary of the Mass.
That which varies is made up of the Introit, the Collect, the Epistle, the Gradual and Gospel, the Offertory, the Secret, the Preface, the Communion (prayer) and the Post communion. The first part of the Mass is known as the Mass of Catechumens, while the second part is called the Mass of the Faithful.”
– Fr Gebhard, 1952