1. The Paschal Mystery: a living and life-giving mystery
Jesus' words and actions during his hidden life in Nazareth and his public ministry were saving acts that anticipated the fullness of his paschal mystery. “When his Hour comes he lives out the unique event in history which does not pass away: Jesus dies, is buried, rises from the dead and is seated at the right hand of the Father once for all (Rom 6:10; Heb 7:27; 9:12). His Paschal Mystery is a real event that occurred in our history, but it is unique: all other historical events happen once, and then they pass away swallowed up in the past. The Paschal mystery of Christ, by contrast, cannot remain only in the past because by his death he destroyed death. All that Christ is—all that he did and suffered for men—participates in the divine eternity and so transcends all times while being made present in them all. The event of the Cross and Resurrection abides and draws everything to life" ( Catechism of the Catholic Church – CCC – 1085).
As Benedict XVI wrote, “Being a Christian starts with the encounter with an event, a Person, which gives life a new horizon and a decisive direction."  Hence “our Faith and the Eucharistic liturgy both have their source in the same event: Christ's gift of himself in the Paschal Mystery." 
2. The Paschal Mystery in the time of the Church: liturgy and sacraments
Christ our Lord “carried out the redemption of humanity principally by the Paschal Mystery of his blessed passion, resurrection from the dead and glorious ascension."  “It is this Mystery that the Church proclaims and celebrates in her liturgy" ( CCC , 1068).
“The liturgy then is rightly seen as an exercise of the priestly office of Jesus Christ. It involves the presentation of man's sanctification under the guise of signs perceptible by the senses and its accomplishment in ways appropriate to each of these signs. In it a full public worship is performed by the Mystical Body of Christ, that is to say by the Head and his members."  “The whole liturgical life of the Church revolves around the Eucharistic sacrifice and the sacraments" (CCC , 1113).
“Seated at the right hand of the Father and pouring out the Holy Spirit on his Body which is the Church, Christ now acts through the sacraments he instituted to communicate his grace" ( CCC, 1084).
2.1. The sacraments: nature, origin and number
“The sacraments are efficacious signs of grace, instituted by Christ and entrusted to the Church, by which divine life is dispensed to us. The visible rites by which the sacraments are celebrated signify and make present the graces proper to each sacrament" ( CCC, 1131). “The sacraments are perceptible signs (actions, words) accessible to our human nature" (CCC, 1084).
“Adhering to the doctrine of the scriptures, apostolic traditions and the unanimous sentiment of the Fathers," we profess that “the sacraments of the new Law were all instituted by our Lord Jesus Christ." 
“There are seven sacraments in the Church: Baptism, Confirmation or Chrismation, Eucharist, Penance, Anointing of the Sick, Holy Orders, and Matrimony" (CCC, 1113). “The seven sacraments touch all the stages and all the important moments of Christian life; they give birth and increase, healing and mission to the Christian life of faith. There is thus a certain resemblance between the stages of natural life and the stages of the spiritual life" ( CCC, 1210). They form an organic whole centered on the Eucharist, which contains the very Author of the sacraments (cf. CCC, 1211).
The sacraments signify three things: the sanctifying cause , which is the Death and Resurrection of Christ; the sanctifying effect or grace; the sanctifying end , which is eternal glory. “A sacrament is a sign that commemorates what preceded it: Christ's Passion; it demonstrates what is accomplished in us through Christ's Passion: grace; and it prefigures what the Passion pledges to us: future glory." 
The sacramental sign, proper to each sacrament, is made up of material realities (water, oil, bread, wine) and human gestures (washing, anointing, laying on of hands, etc.) which are called the matter ; and also of words said by the minister of the sacrament, which are called the form . In reality, “a sacramental celebration is a meeting of God's children with their Father, in Christ and the Holy Spirit; this meeting takes the form of a dialogue through actions and words" ( CCC, 1153).
The liturgy of the sacraments contains an unchangeable part (what Christ himself established about the sacramental sign), and parts that the Church can change for the good of the faithful and greater veneration of the sacraments, adapting them to the circumstances of place and time.  “No sacramental rite may be modified or manipulated at the will of the minister or the community" ( CCC , 1125).
2.2 The effects and necessity of the sacraments
All the sacraments confer sanctifying grace on those who place no obstacles.  This grace “is the gift of the Holy Spirit who justifies us and sanctifies us" ( CCC , 2003). In addition, the sacraments confer the sacramental grace that is proper to each sacrament (cf. CCC, 1128): this is a specific divine help to obtain the aim of the particular sacrament.
We receive not only sanctifying grace, but the Holy Spirit himself. “Through the Church's sacraments, Christ communicates his Holy and sanctifying Spirit to the members of his Body" ( CCC, 739).  The result of the sacramental life is that the Holy Spirit “deifies" the faithful, uniting them in a living union with Christ (cf. CCC , 1129).
The three sacraments of Baptism, Confirmation and Holy Orders, in addition to conferring grace, confer a sacramental character, an indelible spiritual seal impressed on the soul,  by which a Christian shares in Christ's priesthood and is made a member of the Church according to different states and functions. The sacramental character remains for ever as a positive disposition for grace, as a promise and guarantee of divine protection, and as a vocation to divine worship and the service of the Church. For this reason these three sacraments cannot be repeated (cf. CCC, 1121).
The sacraments that Christ has given his Church are necessary (at least the desire to receive them) for salvation and for obtaining sanctifying grace; and none of them is superfluous, even though not all of them are necessary for everyone. 
2.3 Effectiveness of the sacraments
The sacraments “are effective because in them Christ himself is at work; it is he who baptises, he who acts in his sacraments in order to communicate the grace that each sacrament signifies" ( CCC, 1127). The sacramental effect is produced ex opere operato (by the very fact of the action, the sacramental sign, being performed).  “The sacrament does not act in virtue of the justice of the one who gives it or who receives it; it acts by the power of God."  "From the moment that a sacrament is celebrated in accordance with the intention of the Church, the power of Christ and his Spirit acts in and through it, independently of the holiness of the minister" ( CCC , 1128).
The person who administers the sacrament puts himself at the service of Christ and the Church, which is why he is called the minister of the sacrament; and this person cannot be just any member of the faithful, but ordinarily requires the special configuration to Christ the Priest that is given by Holy Orders. 
The effectiveness of the sacraments derives from Christ himself who acts in each sacrament; “nevertheless the fruits of the sacraments also depend on the disposition of the one who receives them" (CCC , 1129). The stronger one's faith, the deeper one's conversion of heart and adhesion to the will of God, the more abundant are the effects of grace that one receives (cf. CCC , 1098).
“Holy Mother Church has, moreover, instituted sacramentals. These are sacred signs that bear a resemblance to the sacraments. They signify effects, particularly of a spiritual nature, which are obtained through the intercession of the Church. By them men are disposed to receive the chief effects of the sacraments, and various occasions of life are rendered holy."  “Sacramentals do not confer the grace of the Holy Spirit in the way that the sacraments do, but by the Church's prayer they prepare us to receive grace and predispose us to co-operate with it" ( CCC, 1670). “Among sacramentals, blessings (of persons, meals, objects and places) come first" (CCC , 1671).
3. The Liturgy
Christian liturgy “is essentially an actio Dei , an action of God which draws us into Christ through the Holy Spirit;"  and it has a dual dimension, ascending and descending.  “The liturgy is an 'action' of the whole Christ ( Christus totus )" (CCC, 1136), and thus “it is the whole community, the Body of Christ united with its Head, that celebrates" ( CCC , 1140). In the midst of the assembly Christ himself is present (cf. Mt 18:20), risen and glorious. Christ presides over the celebration. He, who acts inseparably united to the Holy Spirit, convokes, unites, and teaches the assembly. He, the Eternal High Priest, is the principle protagonist of the ritual action that makes present the salvific event, while making use of his ministers to re-present (to make present, really and truly, in the here and now of the liturgical celebration) his redeeming sacrifice, and to make us sharers in the life-giving gifts of his Eucharist.
While forming “as it were one mystical person" with Christ the Head,  the Church acts in the sacraments as a “priestly society" that is “organically structured." Thanks to Baptism and Confirmation the priestly people become able to celebrate the liturgy. Therefore “liturgical services are not private functions, but are celebrations of the Church…and pertain to the whole Body of the Church. They manifest it, and have effects upon it. But they touch individual members of the Church in different ways, depending on their orders, their role in the liturgical services, and their actual participation in them." 
The whole Church, in heaven and on earth, God and men, takes part in each liturgical celebration (cf. Rev 5). Christian liturgy, even though it may take place solemnly here and now in a specific place and express the yes of a particular community, is by its very nature “catholic." In union with the Pope, with the bishops in communion with the Roman Pontiff, and with the faithful of all times and places, the liturgy is directed towards all mankind, so that God be all in all ( 1 Cor 15:28). Hence this fundamental principle: the true subject of the liturgy is the Church, specifically the communion sanctorum , the communion of saints of all places and times.  Therefore, the more fully a celebration is imbued with this awareness, the more specifically does it fulfil the spirit of the liturgy. One expression of this awareness of the unity and universality of the Church is the use of Latin and Gregorian chant in some parts of the liturgical celebration. 
Thus we can say that the assembly that celebrates is the community of the baptised who “by regeneration and the anointing of the Holy Spirit are consecrated to be a spiritual house and a holy priesthood, that through all the works of Christian faithful they may offer spiritual sacrifices."  This “common priesthood" is that of Christ, the Eternal High Priest, shared in by all his members.  “Thus in the celebration of the sacraments all the assembly is leitourgos , each one according to their function, but in the unity of the Holy Spirit who acts in all" (CCC , 1144). For this reason taking part in liturgical celebrations, even though it does not encompass the entire supernatural life of the faithful, constitutes for them, as for the entire Church, the summit to which all their activity tends and the source from which they draw their strength.  For “the Church receives and at the same time expresses what she herself is in the seven sacraments, thanks to which God's grace concretely influences the lives of the faithful, so that their whole existence, redeemed by Christ, can become an act of worship pleasing to God." 
When we refer to the assembly as the “subject" of the liturgical celebration, we mean that each of the faithful, acting as a member of the assembly, carries out what and only what corresponds to him or her. The members do not all have the same function ( Rom 12:4) Some are called by God in and through the Church to a special service of the community. These servants are chosen by the sacrament of Holy Orders, by which the Holy Spirit configures them to Christ the Head for the service of all the members of the Church.  As John Paul II clarified on several occasions, “ in persona Christi means more than offering 'in the name of' or 'in the place of' Christ. In persona means in specific sacramental identification with the Eternal High Priest who is the author and the principle subject of this sacrifice of his, a sacrifice in which, in truth, nobody can take his place."  As the Catechism graphically says, “the ordained minister is, as it were, the icon of Christ the priest" ( CCC , 1142).
“The mystery celebrated in the liturgy is one, but the forms of its celebrations are diverse. The mystery of Christ is so unfathomably rich that it cannot be exhausted by its expression in any single liturgical tradition" ( CCC , 1200-1201). The liturgical rites presently in use in the Church are the Latin (principally the Roman rite, but also the rites of certain local churches, such as the Ambrosian rite, or those of certain religious orders) and the Byzantine, Alexandrian or Coptic, Syriac, Armenian, Maronite and Chaldean rites" (CCC, 1203). “Holy Mother Church holds all lawfully recognised rites to be of equal right and dignity, and wishes to preserve them in the future and to foster them in every way." 
Juan Jose Silvestre
Catechism of the Catholic Church , nos. 1066-1098; 1113-1143; 1200-1211 and 1667-1671.
Saint Josemaría, Homily “The Eucharist, Mystery of Faith and Love," in Christ is Passing By , nos 83-94; cf. also Conversations , no. 115.
Joseph Ratzinger, The Spirit of the Liturgy , Ignatius Press.
 Benedict XVI, Enc. Deus Caritas Est , 25 December 2005.
 Benedict XVI, Sacramentum Caritatis , 22 February 2007.
 Vatican II, Sacrosantum Concilium , 5; cf. also CCC 1067.
 Ibid ., no 7. CCC , 1070.
 Council of Trent: DZ 1600 – 1601; cf. also CCC, 1114.
 St Thomas Aquinas, Summa Theologiae , III, q.60, a 3; cf. also CCC , 1130.
 Cf. CCC , 1205; Council of Trent: DZ 1728; Pius XII: DZ 3857.
 Cf. Council of Trent: DZ 1606.
 “The desire and work of the Holy Spirit in the heart of the Church is that we may live from the life of the risen Christ" ( CCC, 1091). “He unites the Church to the life and mission of Christ" ( CCC, 1092); “the Holy Spirit heals and transforms those who receive him by conforming them to the Son of God" ( CCC, 1129).
 Cf. Council of Trent: DZ 1609.
 Ibid ., DZ 1604.
 Ibid ., DZ 1608.
 St Thomas Aquinas, Summa Theologiae , III, q.68 art.8.
 The ordained priesthood “guarantees that it really is Christ who acts in the sacraments through the Holy Spirit for the Church. The saving mission entrusted by the Father to his incarnate Son was committed to the apostles and through them to their successors: they receive the Spirit of Jesus to act in his name and in his person. (cf. Jn 20:21-23; Lk 24:47; Mt 28:18-20). The ordained minister is the sacramental link that ties the liturgical action to what the apostles said and did and through them to the words and actions of Christ, source and foundation of the sacraments" ( CCC , 1120). Even though the effectiveness of the sacrament does not depend on the moral qualities of the minister, nevertheless his faith and devotion, as well as contributing to his own personal sanctification, can be of considerable help to foster the good dispositions of the recipient of the sacrament and in consequence the fruit obtained.
 Vatican II,. Sacrosanctum Concilium , 60; (cf. CCC, 1667).
 Benedict XVI, Sacramentum Caritatis , 37
 “On the one hand, the Church, united with her Lord and 'in the Holy Spirit' ( Lk 10:21), blesses the Father 'for his inexpressible gift' (2 Cor 9:15) in her adoration, praise and thanksgiving. On the other hand, until the consummation of God's plan, the Church never ceases to present to God the Father the offering of his own gifts, and to beg him to send the Holy Spirit upon that offering, upon herself, upon the faithful and upon the whole world, so that through communion in the death and resurrection of Christ the Priest, and by the power of the Holy Spirit, these divine blessings will bring forth the fruits of life, 'to the praise of his glorious grace' (Eph 1:6)" (CCC , 1083).
 Cf. Pius XII, Enc. Mystici Corporis (quoted in CCC , 1119).
 Vatican II,. Sacrosanctum Concilium , 26 (quoted in CCC, 1140).
 “May this sacrifice be effective for all mankind-- Orate, fratres, the priest invites the people to pray--because this sacrifice is yours and mine, it is the sacrifice of the whole Church. Pray, brethren, although there may not be many present, although materially there may be only one person there, although the celebrant may find himself alone, because every Mass is a universal sacrifice, the redemption of every tribe and tongue and people and nation (cf. Rev 5:9).
“Through the communion of the saints, all Christians receive grace from every Mass that is celebrated, regardless of whether there is an attendance of thousands of persons or whether it is only a boy with his mind on other things who is there to serve. In either case, heaven and earth join with the angels of the Lord to sing Sanctus, Sanctus, Sanctus… " (St Josemaria Escriva, Christ is Passing By , no 89).
 Benedict XVI, Sacramentum Caritatis , 62; Vatican II, Sacrosanctum Concilium , 54.
 Vatican II, Lumen Gentium , 10.
 Ibid . 10 and 34; Decr. Presbyterorum Ordinis , 2.
 Cf. Vatican II Sacrosanctum Consilium , 20.
 Benedict XVI, Sacramentum Caritatis , 16.
 Cf. Vatican II, Presbyterorum Ordinis , 2 and 15.
 John Paul II, Enc. Ecclesia de Eucharistia , 29. Footnote 59 cites the following words from Pius XII's encyclical Mediator Dei : “The minister of the altar acts in the person of Christ in as much as he
is head, making an offering in the name of all the members."
 Vatican II, Sacrosanctum Concilium. 4.