281. In what way does the Church participate in the eucharistic sacrifice?In the Eucharist the sacrifice of Christ becomes also the sacrifice of the members of his Body. The lives of the faithful, their praise, their suffering, their prayers, their work, are united to those of Christ. In as much as it is a sacrifice, the Eucharist is likewise offered for all the faithful, living and dead, in reparation for the sins of all and to obtain spiritual and temporal benefits from God. The Church in heaven is also united to the offering of Christ.
Further reading: CCC 1368-1372, 1414282. How is Christ present in the Eucharist?
Jesus Christ is present in the Eucharist in a unique and incomparable way. He is present in a true, real and substantial way, with his Body and his Blood, with his Soul and his Divinity. In the Eucharist, therefore there is present in a sacramental way, that is, under the Eucharistic species of bread and wine, Christ whole and entire, God and Man.
Further reading: CCC 1373-1375, 1413