In the early Church, the Liturgy of the Catechumens (those who are undertaking instruction but have yet to be baptized) ended with their expulsion from the congregation. They were not admitted to the Holy Mystery, the Blessed Sacrament itself until they were baptized. The Liturgy of the Faithful begins where instruction ends, with the Offertory.
To emphasize the difference between the Mass of the Catechumens and the Mass of the Faithful, some parishes distinguish between the Little Entrance, during which clergy, assistants, and choristers enter the nave of the Church and process to the altar; and the Great Entrance, during which the sacred elements of bread and wine (along with the money offering which for most of us now substitutes for bread and wine) are brought forward by lay representatives of the people.
Where “Little Entrance” is the only Entrance, representatives of the people bring forward the money that has been collected and present it to acolytes who, in turn, carry it to the priest. Acolytes, acting as representatives of the people, present the sacred elements (which the altar guild has placed on the credence table) to the priest.
Note: Anglicans will be interested to know that the Great Entrance was introduced to the Liturgy through the Sarum Rite.