Chapter II-A. General Structure of the Mass
7. At Mass or the Lord's Supper, the people of God are called together, with a priest presiding and acting in the person of Christ, to celebrate the memorial of the Lord or eucharistic sacrifice.  For this reason Christ's promise applies supremely to such a local gathering together of the Church: "Where two or three come together in my name, there am I in their midst" (Mt 18:20). For at the celebration of Mass, which perpetuates the sacrifice of the cross,  Christ is really present to the assembly gathered in His name; He is present in the person of the minister, in His own word, and indeed substantially and permanently under the eucharistic elements. 
8. The Mass is made up as it were of the Liturgy of the Word and the Liturgy of the Eucharist, two parts so closely connected that they form but one single act of worship.  For in the Mass the table of God's word and of Christ's body is laid for the people of God to receive from it instruction and food.  There are also certain rites to open and conclude the celebration.