Holy Mass has two large parts. The first part is called The Mass of the Catechumens. It consists of the prayers and readings from the beginning of Mass to the Offertory.
The word catechumens is a very old word. Long ago people who were preparing to receive the Sacrament of Baptism were called catechumens or learners. During the time of instruction, they were permitted to be present only at the first part of the Mass. They had to leave after the sermon. It was in this way that the first part of the Mass received the name, “Mass of the Catechumens” or the “Mass of the Learners.”
The second part of Holy Mass is called The Mass of the Faithful. This part of the Mass begins with the Offertory and continues to the end of Holy Mass.
The word faithful means baptized Christians. For several hundred years, only the baptized were allowed to assist at the second part of Holy Mass.
There is another division of the parts of Holy Mass. One part is called the Ordinary of the Mass. The other part is called the Proper of the Mass.
The Ordinary of the Mass is made up of the prayers which, with few exceptions, do not change. The Proper consists of the prayers and readings that change from day to day.
Taken from The Kingdom of God series The Holy Sacrifice of the Mass by Ellamay Horan. I am not the Author merely the distributor. God Bless BJS!!