Catechism of the Catholic Church
The presence of Christ by the power of his word and the Holy Spirit
1373 "Christ Jesus, who died, yes, who was raised from the dead, who is at the right hand of God, who indeed intercedes for us," is present in many ways to his Church:195 in his word, in his Church's prayer, "where two or three are gathered in my name,"196 in the poor, the sick, and the imprisoned,197 in the sacraments of which he is the author, in the sacrifice of the Mass, and in the person of the minister. But "he is present . . . most especially in the Eucharistic species."198
1374 The mode of Christ's presence under the Eucharistic species is unique. It raises the Eucharist above all the sacraments as "the perfection of the spiritual life and the end to which all the sacraments tend."199 In the most blessed sacrament of the Eucharist "the body and blood, together with the soul and divinity, of our Lord Jesus Christ and, therefore, the whole Christ is truly, really, and substantially contained."200 "This presence is called 'real' - by which is not intended to exclude the other types of presence as if they could not be 'real' too, but because it is presence in the fullest sense: that is to say, it is a substantial presence by which Christ, God and man, makes himself wholly and entirely present."201
1375 It is by the conversion of the bread and wine into Christ's body and blood that Christ becomes present in this sacrament. the Church Fathers strongly affirmed the faith of the Church in the efficacy of the Word of Christ and of the action of the Holy Spirit to bring about this conversion. Thus St. John Chrysostom declares:
It is not man that causes the things offered to become the Body and Blood of Christ, but he who was crucified for us, Christ himself. the priest, in the role of Christ, pronounces these words, but their power and grace are God's. This is my body, he says. This word transforms the things offered.202
and St. Ambrose says about this conversion:
Be convinced that this is not what nature has formed, but what the blessing has consecrated. the power of the blessing prevails over that of nature, because by the blessing nature itself is changed.... Could not Christ's word, which can make from nothing what did not exist, change existing things into what they were not before? It is no less a feat to give things their original nature than to change their nature.203
1376 The Council of Trent summarizes the Catholic faith by declaring: "Because Christ our Redeemer said that it was truly his body that he was offering under the species of bread, it has always been the conviction of the Church of God, and this holy Council now declares again, that by the consecration of the bread and wine there takes place a change of the whole substance of the bread into the substance of the body of Christ our Lord and of the whole substance of the wine into the substance of his blood. This change the holy Catholic Church has fittingly and properly called transubstantiation."204
1377 The Eucharistic presence of Christ begins at the moment of the consecration and endures as long as the Eucharistic species subsist. Christ is present whole and entire in each of the species and whole and entire in each of their parts, in such a way that the breaking of the bread does not divide Christ.205
1378 Worship of the Eucharist. In the liturgy of the Mass we express our faith in the real presence of Christ under the species of bread and wine by, among other ways, genuflecting or bowing deeply as a sign of adoration of the Lord. "The Catholic Church has always offered and still offers to the sacrament of the Eucharist the cult of adoration, not only during Mass, but also outside of it, reserving the consecrated hosts with the utmost care, exposing them to the solemn veneration of the faithful, and carrying them in procession."206
1379 The tabernacle was first intended for the reservation of the Eucharist in a worthy place so that it could be brought to the sick and those absent outside of Mass. As faith in the real presence of Christ in his Eucharist deepened, the Church became conscious of the meaning of silent adoration of the Lord present under the Eucharistic species. It is for this reason that the tabernacle should be located in an especially worthy place in the church and should be constructed in such a way that it emphasizes and manifests the truth of the real presence of Christ in the Blessed Sacrament.
1380 It is highly fitting that Christ should have wanted to remain present to his Church in this unique way. Since Christ was about to take his departure from his own in his visible form, he wanted to give us his sacramental presence; since he was about to offer himself on the cross to save us, he wanted us to have the memorial of the love with which he loved us "to the end,"207 even to the giving of his life. In his Eucharistic presence he remains mysteriously in our midst as the one who loved us and gave himself up for us,208 and he remains under signs that express and communicate this love:
The Church and the world have a great need for Eucharistic worship. Jesus awaits us in this sacrament of love. Let us not refuse the time to go to meet him in adoration, in contemplation full of faith, and open to making amends for the serious offenses and crimes of the world. Let our adoration never cease.209
1381 "That in this sacrament are the true Body of Christ and his true Blood is something that 'cannot be apprehended by the senses,' says St. Thomas, 'but only by faith, which relies on divine authority.' For this reason, in a commentary on Luke 22:19 ('This is my body which is given for you.'), St. Cyril says: 'Do not doubt whether this is true, but rather receive the words of the Savior in faith, for since he is the truth, he cannot lie.'"210
Godhead here in hiding, whom I do adore
Masked by these bare shadows, shape and nothing more,
See, Lord, at thy service low lies here a heart
Lost, all lost in wonder at the God thou art.
Seeing, touching, tasting are in thee deceived;
How says trusty hearing? that shall be believed;
What God's Son has told me, take for truth I do;
Truth himself speaks truly or there's nothing true.211
195 ⇒ Rom 8:34; cf. LG 48.
196 ⇒ Mt 18:20.
197 Cf. ⇒ Mt 25:31-46.
198 SC 7.
199 St. Thomas Aquinas, STh III, 73, 3c.
200 Council of Trent (1551): DS 1651.
201 Paul VI, MF 39.
202 St. John Chrysostom, prod. Jud. 1:6: PG 49, 380.
203 St. Ambrose, De myst. 9, 50; 52: PL 16, 405-407.
204 Council of Trent (1551): DS 1642; cf. ⇒ Mt 26:26 ff.; ⇒ Mk 14:22 ff.; ⇒ Lk 22:19 ff.; ⇒ 1 Cor 11:24 ff.
205 Cf. Council of Trent: DS 1641.
206 Paul VI, MF 56.
207 ⇒ Jn 13:1.
208 Cf. ⇒ Gal 2:20.
209 John Paul II, Dominicae cenae, 3.
210 St. Thomas Aquinas, STh III, 75, 1; cf. Paul VI, MF 18; St. Cyril of
Alexandria, In Luc. 22, 19: PG 72, 912; cf. Paul VI, MF 18.
211 St. Thomas Aquinas (attr.), Adoro te devote; tr. Gerard Manley