Part I. General Principles to be Given Prominence in Catechizing the People on the Eucharistic Mystery
Requirements of Pastors who are to Give Instruction About this Mystery
5. Effective catechises is necessary so that the eucharistic mystery might suffuse integral teaching of faith, which is contained in the documents of the magisterium,
but also with heart and life enter deeply into the spirit of the Church on this matter.  Then they will more readily judge which of the many aspects of this mystery
best suits the faithful in any given situation.
In view of what was said in no. 3, the following points, among others, deserve special attention.
The Eucharistic Mystery as Center of the Whole Life of the Church
6. Catechesis to the eucharistic mystery should aim at helping the faithful realize deeply that its celebration is the true center of the whole Christian life, both for the
universal Church and for the local congregations of that Church. For "the other sacraments, like every ministry of the Church and every work of the apostolate, are linked
wit the holy eucharist and have it as their end. For the most blessed eucharist contains the Church's entire spiritual wealth, that is,
Christ himself. He is our Passover and living bread; through his flesh, made living and life-giving by the Holy Spirit, he is giving people life and thereby inviting and leading
them to offer themselves together with him, as well as their labors and all created things." 
The eucharist is the effective sign and sublime cause of the sharing in divine life and the unity of the people of God by which the Church exists.  It is the culmination both
of God's action sanctifying the world in Christ and of the worship we offer to Christ and through him to the Father in the Holy Spirit.  Its celebration "is the outstanding
means whereby the faithful may express in their lives and manifest in others the mystery of Christ and the real nature of the true Church." 
The Eucharistic Mystery As the Center of the Local Church
7. Through the eucharist "the Church continually lives and grows. This Church of Christ is truly present in all lawful, local congregations of the faithful, which, united with their
bishops, are themselves called Churches in the New Testament. For in their own locality these Churches are the new people called by God in the Holy Spirit and in great fullness (see 1 Thes 1:5).
In them the faithful are gathered together through the preaching of Christ's Gospel and the mystery of the Lord's Supper is celebrated, so that 'through the meal of the body and blood of the
Lord the whole brotherhood is joined together.'  Any community of the altar, under the sacred ministry of the bishop,"  or of a priest who takes his place,  "stands out clearly as a symbol of that charity and 'unity of the Mystical Body without which there can be no salvation.'  In these communities, though frequently small and poor or living in isolation, Christ is present and the power of his presence gathers together the one, holy, catholic, and apostolic Church. For 'the sharing of the body and blood of Christ does nothing less than transform us into what we receive." , 
The Eucharistic Mystery and the Unity of Christians
8. In addition to those things that concern the ecclesial community and the individual faithful, pastors should pay special attention to that part of the doctrine in which the Church teaches that the memorial of the Lord, celebrated in accord with his will, signifies and brings about the unity of all who believe in him. 
In compliance with the Decree on Ecumenism of Vatican Council II,  the faithful should be led to a proper appreciation of the values that are preserved in the eucharistic traditional through which their brothers and sisters in other Christian Confessions have continued to celebrate the Lord's Supper. For "when in the Lord's Supper they commemorate his death and resurrection, they attest to the sign of their life in communion with Christ and they await his glorious Second Coming."  Those, moreover, who have preserved the sacrament of orders in the celebration of the eucharist, "united with the bishop and having access to God the Father through the Word incarnate, crucified and glorified, attain communion with the Trinity by the outpouring of the Holy Spirit as people who have become 'partakers in the divine nature' (2 Pt 1:4). In each of these Churches, therefore, the celebration of the eucharist builds up and gives increase 'to the Church of God and its concelebration shows forth the communion of these Churches with each other." 
Above all in the celebration of the mystery of unity all Christians should be filled with sadness over the divisions separating them. Therefore, they should fervently pray to God that all Christ's disciples may daily come to a deeper understanding of the eucharistic mystery conformed to his own mind. They should celebrate in such a way that, made partakers in the body of Christ, they may become one Body (see 1 Cor 10:17), "linked by those same bonds with which he himself desired it to be joined." 
The Different Modes of Christ's Presence
9. In order to achieve a deeper understanding of the eucharistic mystery, the faithful should be instructed in the principal modes by which the Lord is present to his Church in liturgical celebrations. 
He is always present in an assembly of the faithful gathered in his name (see Mt 18:20). He is also present in his word, for it is he who is speaking as the sacred Scriptures are read in the Church.
In the eucharistic sacrifice he is present both in the person of the minister, "the same now offering through the ministry of the priest who formerly offered himself on the cross,"  and above all under the eucharistic elements.  For in that sacrament, in a unique way, Christ is present, whole and entire, God and man, substantially and continuously. This presence of Christ under the elements "is called the real presence not to exclude the other kinds, as though they were no real, but because it is real par excellence." 
Connection Between the Liturgy of the Word and the Liturgy of the Eucharist
10. Pastors should, therefore, "insistently teach the faithful to take their part in the entire Mass," by showing the close connection that exists between the liturgy of the word and the celebration of the Lord's Supper, so that they may clearly perceive how the two constitute a single act of worship.  "The preaching of the word is necessary for the administration of the sacraments. For the sacraments are sacraments of faith and faith has its origin and substance in the word."  This is especially true of the celebration of Mass, in which the purpose of the liturgy of the word is to develop in a specific way the close link between the proclamation and hearing of the word of God and the eucharistic mystery. 
The faithful, therefore, hearing the word of God, should realize that the wonders it proclaims achieve their summit in the paschal mystery, whose memorial is celebrated sacramentally in the Mass. In this way, the faithful, receiving the word of God and nourished by it, will be led in a spirit of thanksgiving to a fruitful participation in the mysteries of salvation. In this way the Church feeds upon the bread of life as it comes from the table of both the word of God and the body of Christ. 
The Universal Priesthood and the Ministerial Priesthood in the Celebration of the Eucharist
11. The more clearly the faithful recognize the place they have in the liturgical assembly and the parts they are to fulfill in the eucharistic celebration the more conscious and fruitful will be the active participation that belongs to a community. 
Catechesis, then, should explain the teachings on the royal priesthood, which consecrates the faithful through their rebirth and the anointing of the Holy Spirit. 
There should also be further explanation both of the role of the ministerial priesthood in the celebration of the eucharist, which differs from the universal priesthood of the faithful in essence and not merely in degree,  and of the parts fulfilled by others who exercise some ministry. 
The Nature of Active Participation in the Mass
12. It should be explained that all who gather for the eucharist are that holy people who, together with the ministers, have a part in the sacred rites. The priest alone, insofar as he acts in the person of Christ, consecrates the bread and wine. Nevertheless the active part of the faithful in the eucharist consists in: giving thanks to God as they are mindful of the Lord's passion, death, and resurrection; offering the spotless victim not only through the hands of the priest but also together with him; and, through the reception of the body of the Lord, entering into the Communion with God and with each other that participation is meant to lead to.  For there is a fuller share in the Mass when the people, properly disposed, receive the body of the Lord sacramentally in the Mass itself, out of obedience to his own words: "Take and eat," 
Like Christ's own passion, this sacrifice, though offered for all, "has no effect except in those who are united to Christ's passion by faith and charity . . . Even for these, its benefits are greater or less in proportion to their devotion." 
All these things should be explained to the faithful in such a way that in consequence they share actively in the celebration of the Mass by both their inner affections and the outward rites, in keeping with the principles laid down by the Constitution on the Liturgy,  which have been further specified by the Instruction Inter Oecumenici of 26 September 1964, the Instruction Musicam sacram of 5 March 1967,  and the Instruction Tres abhinc annos of 4 May 1967.
Influence of the Eucharistic Celebration on the Daily Life of the Faithful
13. What the faithful have received through faith and the sacrament in the celebration of the eucharist they should hold to by the way they live. They should strive to live their whole lives joyfully in the strength of this heavenly food, as sharers in the death and resurrection of the Lord. After taking part in the Mass therefore all should be "eager to do good works, to please God, and to live rightly, devoted to the Church, putting into practice what they have learned and growing in devotion."  They will seek to fill the world with the Christian spirit and "in all things, even in the midst of human affairs," to become witnesses of Christ. 
For "no Christian community is ever built up unless it has its roots and center in the eucharistic liturgy, which, therefore, is the indispensable starting point for leading people to a sense of community." 
Catechesis for Children on the Mass
14. Those who take care of the religious instruction of children, especially parents, pastors, and teachers, should be careful, when introducing them gradually to the mystery of salvation,  to give catechesis on the Mass the importance it deserves. This catechesis, suited to children's age and capacities, should, by means of the main rites and prayers of the Mass, aim at conveying its meaning, including what relates to taking part in the Church's life.
All these things should be kept in mind in the special situation of preparing children for first communion, so that it will be very clear to them that this communion is their complete incorporation into the Body of Christ. 
The Rites and Prayers as Starting Points for Catechesis on the Mass
15. The Council of Trent prescribes that pastors should frequently "either themselves or through others, elaborate on some part of what is read at Mass and, among other things, explain something of the mystery of this sacrament." 
Pastors should therefore guide the faithful to a full understanding of this mystery of faith by suitable catechesis, which should take as its starting point the mysteries of the liturgical year and the rites and prayers that are part of the celebration. Pastors should do this by explaining the meaning of these rites and prayers, especially those of the great eucharistic prayer, and lead the people to grasp the mystery that the rites and prayers signify and accomplish.