Theological Richness: Like the liturgies of the Eastern Church, both Catholic and Orthodox, the Tridentine Latin Mass is very rich theologically. The concept of the Mass as a mystical reality in which the sacrifice of Christ on the Cross is renewed is very evident in the text. As the Council of Trent declared, "The same Christ who offered himself once in a bloody manner on the altar of the cross, is present and offered in an unbloody manner" in the Mass. There is little room for departure from the rubrics (rules) of the Tridentine Latin Mass, and the prayers and readings for each feast are strictly prescribed.

The term “the Latin Mass” is most often used to refer to the Tridentine Mass—the Mass of Pope St. Pius V, promulgated on July 14, 1570, through the apostolic constitution Quo Primum. Technically, this is a misnomer; any Mass celebrated in Latin is a “Latin Mass.” However, after the promulgation of the Novus Ordo Missae, the Mass of Pope Paul VI, in 1969, which allowed for more frequent celebration of Mass in the vernacular for pastoral reasons, the term has come to be used almost exclusively to refer to the traditional Latin Mass—the Tridentine Mass.

The Ancient Liturgy of the Western Church:

Even the phrase “the Tridentine Mass” is somewhat misleading. It takes its name from the Council of Trent (1545-63), which was called largely in response to the rise of Protestantism in Europe. The council addressed many issues, however, including the proliferation of modifications of the traditional Latin Rite Mass. While the essentials of the Mass had remained constant since the time of Pope St. Gregory the Great (590-604), many dioceses and religious orders (particularly the Franciscans) had modified the calendar of feasts by adding numerous saints’ days.

Standardizing the Mass:

At the direction of the Council of Trent, Pope St. Pius V imposed a revised missal (the instructions for celebrating the Mass) upon all Western dioceses and religious orders that could not show that they had used their own calendar or modified liturgical text for at least 200 years. (Eastern Churches in union with Rome retained their traditional liturgies and calendars.)
In addition to standardizing the calendar, the revised missal required an entrance psalm (the Introibo and Judica Me) and a penitential rite (the Confiteor), as well as the reading of the Last Gospel (John 1:1-14) at the end of Mass.

Theological Richness:

Like the liturgies of the Eastern Church, both Catholic and Orthodox, the Tridentine Latin Mass is very rich theologically. The concept of the Mass as a mystical reality in which the sacrifice of Christ on the Cross is renewed is very evident in the text. As the Council of Trent declared, "The same Christ who offered himself once in a bloody manner on the altar of the cross, is present and offered in an unbloody manner" in the Mass.
There is little room for departure from the rubrics (rules) of the Tridentine Latin Mass, and the prayers and readings for each feast are strictly prescribed.

Instruction in the Faith:

The traditional missal functions as a living catechism of the Faith; over the course of one year, the faithful who attend the Tridentine Latin Mass and follow the prayers and readings receive a thorough instruction in all of the essentials of Christian belief, as taught by the Catholic Church, as well as in the lives of the saints.
To make it easier for the faithful to follow along, many prayer-books and missals were printed with the text of the Mass (as well as the daily prayers and readings) in both Latin and the vernacular, the local language.

Differences From the Current Mass:

For most Catholics who are used to the Novus Ordo, the version of the Mass used for the last 40 years, there are obvious differences from the Tridentine Latin Mass. While Pope Paul VI merely allowed for the use of the vernacular and for the celebration of the Mass facing the people (rather than facing a high altar, in the same direction that the people face), both conditions have now become standard. The Tridentine Latin Mass offered only one Eucharistic Prayer (the Roman Canon), while six such prayers have been approved for use in the new Mass, and others have been added locally.

Liturgical Diversity or Confusion?:

In some ways, our current situation resembles that at the time of the Council of Trent. Local dioceses—even local parishes—have added Eucharistic Prayers and modified the text of the Mass, practices forbidden by the Church. The celebration of the Mass in the local language and the increased migration of populations has meant that even a single parish may have several Masses on a Sunday that are celebrated in different languages. Some critics argue that these changes have undercut the universality of the Mass, which was evident in the strict adherence to rubrics and the use of Latin in the Tridentine Latin Mass.

Pope John Paul II, the Society of St. Pius X, and Ecclesia Dei:

Addressing these criticisms, and responding to the schism of the Society of St. Pius X (who had continued to celebrate the Tridentine Latin Mass), Pope John Paul II issued a motu proprio on July 2, 1998. The document, entitled Ecclesia Dei, declared that “Respect must everywhere be shown for the feelings of all those who are attached to the Latin liturgical tradition, by a wide and generous application of the directives already issued some time ago by the Apostolic See for the use of the Roman Missal according to the typical edition of 1962”—in other words, for the celebration of the Tridentine Latin Mass.

The Return of the Latin Mass?:

The decision to allow the celebration was left up to the local bishop, and, over the next 15 years, some bishops made a “generous application of the directives” while others did not. John Paul’s successor, Pope Benedict XVI, has long expressed his desire to see a wider use of the Tridentine Latin Mass, and, on June 28, 2007, the Press Office of the Holy See announced that he will release a motu proprio of his own, within a few day, that will allow all priests to celebrate the Tridentine Latin Mass in private and to hold public celebrations when requested even by a relatively small number   of the faithful in a parish.
Pope Benedict’s actions parallels other initiatives of his pontificate, including a new English translation of the Novus Ordo to bring out some of the theological richness of the Latin text that is missing in the current translation, the curbing of abuses in the celebration of the Novus Ordo, and the encouragement of the use of Latin and Gregorian chant in the celebration of the Novus Ordo. The Pope has also expressed his belief that a wider celebration of the Tridentine Latin Mass will allow the older Mass to act as a standard for the celebration of the newer one.

fonte:http://catholicism.about.com/od/worship/p/The_Latin_Mass.htm