The following are excerpts from Vatican II’s Constitution on the Sacred Liturgy (Sacrosanctum Concilium) that pertain to the Mass and the sacrament of the eucharist.
- For it is the liturgy through which, especially in the divine sacrifice of the Eucharist, “the work of our redemption is accomplished,” and it is through the liturgy, especially, that the faithful are enabled to express in their lives and manifest to others the mystery of Christ and the real nature of the true Church.  The liturgy daily builds up those who are in the Church, making of them a holy temple of the Lord, a dwelling-place for God in the Spirit,  to the mature measure of the fullness of Christ.
CHAPTER I: GENERAL PRINCIPLES FOR THE RESTORATION AND PROMOTION OF THE SACRED LITURGY
- THE NATURE OF THE SACRED LITURGY AND ITS IMPORTANCE IN THE LIFE OF THE CHURCH
But [Jesus] also willed that the work of salvation which [the apostles] preached should be set in train through the sacrifice and sacraments, around which the entire liturgical life revolves. Thus by Baptism men are grafted into the paschal mystery of Christ; they die with him, are buried with him and rise with him.  They receive the spirit of adoption as sons “in which we cry, Abba, Father” (Rom. 8:15) and thus become true adorers such as the Father seeks.  In like manner as often as they eat the Supper of the Lord they proclaim the death of the Lord until he comes.  That was why on the very day of Pentecost when the Church appeared before the world those “who received the word” of Peter “were baptized.” And “they continued steadfastly in the breaking of bread and in prayers … praising God and being in favor with all the people” (Acts 2:41-47). From that time onward the Church has never failed to come together to celebrate the paschal mystery, reading those things “which were in all the scriptures concerning him” (Lk. 24:27), celebrating the Eucharist in which “the victory and triumph of his death are again made present,” and at the same time “giving thanks to God for his inexpressible gift” (2 Cor. 9:15) in Christ Jesus, “in praise of his glory” (Eph. 1:12) through the power of the Holy Spirit.
- To accomplish so great a work Christ is always present in his Church, especially in her liturgical celebrations. He is present in the sacrifice of the Mass not only in the person of his minister, “the same now offering, through the ministry of priests, who formerly offered himself on the cross,”  but especially in the Eucharistic species.
- Nevertheless the liturgy is the summit toward which the activity of the Church is directed; it is also the fount from which all her power flows. For the goal of apostolic endeavor is that all who are made sons of God by faith and baptism should come together to praise God in the midst of his Church, to take part in the Sacrifice and to eat the Lord’s Supper. The liturgy, in its turn, moves the faithful filled with “the paschal sacraments” to be “one in holiness”;  it prays that “they hold fast in their lives to what they have grasped by their faith.”  The renewal in the Eucharist of the covenant between the Lord and man draws the faithful and sets them aflame with Christ’s insistent love. From the liturgy therefore, and especially from the Eucharist, grace is poured forth upon us as from a fountain, and the sanctification of men in Christ and the glorification of God to which all other activities of the Church are directed, as toward their end, are achieved with maximum effectiveness.
We also learn from the same apostle that we must always carry around in our bodies the dying of Jesus, so that the life also of Jesus may be made manifest in our mortal Flesh.  That is why we beg the Lord in the Sacrifice of the Mass that “receiving the offering of the Spiritual Victim” he may fashion us for Himself “as an eternal gift.” 
III THE REFORM OF THE SACRED LITURGY
- In order that the Christian people may more certainly derive an abundance of graces from the sacred liturgy, holy Mother Church desires to undertake with great care a general restoration of the liturgy itself. for the liturgy is made up of unchangeable elements divinely instituted, and of elements subject to change.
A. GENERAL NORMS
- (1) Regulation of the sacred liturgy depends solely on the authority of the Church, that is, on the Apostolic See, and, as laws may determine, on the bishop.
(2) In virtue of power conceded by law, the regulation of the liturgy within certain defined limits belongs also to various kinds of bishops’ conferences, legitimately established, with competence in given territories.
(3) Therefore no other person, not even a priest, may add, remove, or change anything in the liturgy on his own authority.
- In order that sound tradition be retained, and yet the way remain open to legitimate progress, a careful investigation — theological, historical, and pastoral — should always be made into each part of the liturgy which is to be revised.
B. NORMS DRAWN FROM HIERARCHIC AND COMMUNAL NATURE OF THE LITURGY
- In liturgical celebrations each person, minister, or layman who has an office to perform, should carry out all and only those parts which pertain to his office by the nature of the rite and the norms of the liturgy.
CHAPTER II: THE MOST SACRED MYSTERY OF THE EUCHARIST
- At the Last Supper, on the night he was betrayed, our Savior instituted the Eucharistic sacrifice of his Body and Blood. This he did in order to perpetuate the sacrifice of the Cross throughout the ages until he should come again, and so to entrust to His beloved Spouse, the Church, a memorial of his death and resurrection: a sacrament of love, a sign of unity, a bond of charity,  a paschal banquet in which Christ is consumed, the mind is filled with grace, and a pledge of future glory is given to us. 
- The Church, therefore, earnestly desires that Christ’s faithful, when present at this mystery of faith, should not be there as strangers or silent spectators. On the contrary, through a good understanding of the rites and prayers they should take part in the sacred action, conscious of what they are doing, with devotion and full collaboration. They should be instructed by God’s word, and be nourished at the table of the Lord’s Body. They should give thanks to God. Offering the immaculate victim, not only through the hands of the priest but also together with him, they should learn to offer themselves.
- The rite of the Mass is to be revised in such a way that the intrinsic nature and purpose of its several parts, as well as the connection between them, may be more clearly manifested, and that devout and active participation by the faithful may be more easily achieved. For this purpose the rites are to be simplified, due care being taken to preserve their substance. Parts which with the passage of time came to be duplicated, or were added with little advantage, are to be omitted. Other parts which suffered loss through accidents of history are to be restored to the vigor they had in the days of the holy Fathers, as may seem useful or necessary.
- The treasures of the Bible are to be opened up more lavishly so that a richer fare may be provided for the faithful at the table of God’s word. In this way a more representative part of the sacred scriptures will be read to the people in the course of a prescribed number of years.
- By means of the homily the mysteries of the faith and the guiding principles of the Christian life are expounded from the sacred text during the course of the liturgical year. The homily, therefore, is to be highly esteemed as part of the liturgy itself. In fact at those Masses which are celebrated on Sundays and holidays of obligation, with the people assisting, it should not be omitted except for a serious reason.
- The “common prayer” or “prayer of the faithful” is to be restored after the gospel and homily, especially on Sundays and holy days of obligation. By this prayer in which the people are to take part, intercession will be made for holy Church, for the civil authorities, for those oppressed by various needs, for all mankind, and for the salvation of the entire world. 
- A suitable place may be allotted to the vernacular in Masses which are celebrated with the people, especially in the readings and “the common prayer,” and also, as local conditions may warrant, in those parts which pertain to the people, according to the rules laid down in Article 36 of this Constitution. Nevertheless care must be taken to ensure that the faithful may also be able to say or sing together in Latin those parts of the Ordinary of the Mass which pertain to them. Wherever a more extended use of the vernacular in the Mass seems desirable, the regulation laid down in Article 40 of this Constitution is to be observed.
- The more perfect form of participation in the Mass whereby the faithful, after the priest’s communion, receive the Lord’s Body from the same sacrifice, is warmly recommended. The dogmatic principles which were laid down by the Council of Trent remaining intact,  communion under both kinds may be granted when the bishops think fit, not only to clerics and religious but also to the laity, in cases to be determined by the Apostolic See. For example, To the newly ordained in the Mass of their ordination; To the newly professed in the mass of their religious profession; To the newly baptized in the Mass which follows their baptism.
- The two parts which in a sense go to make up the Mass, viz. the liturgy of the word and the Eucharistic liturgy, are so closely connected with each other that they form but one single act of worship. Accordingly this sacred Synod strongly urges pastors of souls that, when instructing the faithful, they insistently teach them to take their part in the entire Mass, especially on Sundays and holy days of obligation.
CHAPTER V: THE LITURGICAL YEAR
- By a tradition handed down from the apostles, which took its origin from the very day of Christ’s resurrection, the Church celebrates the paschal mystery every seventh day, which day is appropriately called the Lord’s Day or Sunday. For on this day Christ’s faithful are bound to come together into one place. They should listen to the word of God and take part in the Eucharist, thus calling to mind the passion, resurrection, and glory of the Lord Jesus, and giving thanks to God who “has begotten them again, through the resurrection of Christ from the dead, unto a living hope” (1 Pet. 1:3).
These excerpts from Vatican II are from the Second Vatican Council’s Constitution on the Sacred Liturgy, Sacrosanctum Concilium. It was the first conciliar Constitution to be promulgated by Pope Paul VI in 1963.