It has been said that the use of any language in itself was immaterial, but in its consequences, or in view of the commands of the Church, it is by no means immaterial. The Church has wisely ordered the Latin tongue only to be used in the Mass and in the administration of the Sacraments, for several reasons.

1. Latin was the language used by St. Peter when he first said Mass at Rome. It was the language in which that Prince of the Apostles drew up the Liturgy which, together with the knowledge of the Gospel, he or his successors the Popes imparted to the different peoples of Italy, France, Belgium, Spain, Portugal, England, Ireland, Scotland, Germany, Hungary, and Poland.
2. From the time of the Apostles down, Latin has invariably been used at the altar through the western parts of Christendom, though their inhabitants very frequently did not understand the language. The Catholic Church, through an aversion to innovations, carefully continues to celebrate her Liturgy in that same tongue which apostolic men and saints have used for a similar purpose during more than eighteen centuries.
3. Unchangeable dogmas require an unchangeable language. The Catholic Church cannot change, because it is the Church of God, Who is unchangeable; consequently the language of the Church must also be unchangeable.
4. Mass is said in Latin because a universal Church requires a universal language. The Catholic Church is the same in every clime, in every nation, and consequently its language must be always and everywhere the same, to secure uniformity in her service.
5. Variety of languages is a punishment, a consequence of sin; it was inflicted by God that the human race might be dispersed over the face of the earth. The holy Church, the immaculate Spouse of Jesus Christ, has been established for the express purpose of destroying sin and uniting all mankind; consequently she must everywhere speak the same language.
6. It is a fact well known that the meaning of the words is changed in the course of time by everyday usage. Words which once had a good meaning are now used in a vulgar or ludicrous sense. The Church, enlightened by the Holy Ghost, has chosen a language which is not liable to such changes. The sermons and instructions, and in short everything that is addressed directly to the people, are all in the language of the country; even the prayers of the Mass are translated in almost every Catholic prayerbook, so that there can be no disadvantage to the Catholic worshipper in the fact that the Mass is celebrated in the Latin tongue; especially as the pastors of the Church are very careful to comply with the injunctions of the Council of Trent, to instruct their flocks on the nature of that great Sacrifice, and to explain to them in what manner they should accompany the officiating priest with prayers and devotions best adapted to every portion of the Mass.
   In the second place, faithful Catholics know well that the Holy Sacrifice of the Mass is the self-same sacrifice that Jesus Christ offered to His Father on the Cross, because both the Priest and the Victim are the same; their faith in the Real Presence is abundantly sufficient to enkindle devotion in their hearts, and to excite in their souls appropriate acts of adoration, thanksgiving and repentance, though they may not understand the prayers which the priest is uttering. For this reason it is that the faithful, pressed by different wants, go to the adorable mysteries of the Mass, never thinking of the language in which they are celebrated. Some, moved by the force of calamities, hasten thither to lay their sorrows at the feet of Jesus. Others go to ask for some grace and special mercy, knowing that the heavenly Father can refuse nothing to His Son. Many feel constrained to fly thither to proclaim their gratitude, and to pour forth the love of a thankful heart, knowing that there is nothing so worthy of being offered to God as the sacred Body and Blood of the eternal Victim. More press forward to give glory to God and to honor His saints, for in the celebration of these mysteries of love alone can we pay worthy homage to His adorable Majesty, while we bear witness to our reverence for those who served Him.
   Lastly, men hasten to Mass on the wings of charity and compassion, for it is there that they can hope to obtain salvation for the living and rest for the dead. Thus to the thirsty pilgrims through the rocks of the desert do the fountains of water appear. Thus do the generation of those who seek justice received benediction from the Lord and mercy from God their Savior.

Pity for those who know not this heavenly Sacrifice! What a misfortune to see one driven from this Eden, and yet to do nothing to obtain the favor of readmittance! How unhappy too are those Catholics who, though knowing it, by their unpardonable indifference deprive themselves of this exhaustless mine of inestimable riches.

The above was taken from Chapter 37 of the book The Holy Sacrifice of the Mass by Fr. Michael Muller, C.SS.R., available from TAN Books.

Objection: If the Mass is in Latin, no one can understand a thing because it is said in a language that is no longer spoken.

Response: It is true that Latin is no longer spoken ordinarily, but in order to follow this Mass without difficulty, bilingual missals are available which have on one side the text of the Latin prayers which the priest says and on the other side the translation in the every day language of the people. With a bit of practice, it is within the reach of everyone to unite himself with the prayers that are said. In addition, to want to understand everything of the Divine Mystery, which is the Sacred Mass, is impossible, mystery by definition is a truth that one cannot fully comprehend.

Conclusion:

"The Church is without question a living organism, and as an organism in respect of the Sacred Liturgy also, she grows, matures, develops, adapts and accommodates herself to temporal needs and circumstances, provided only that the integrity of her doctrine be safeguarded. This notwithstanding, the temerity and daring of those who introduce novel liturgical practices, or call for the revival of obsolete rites out of harmony with laws and rubrics, deserve reproof. It has pained Us grievously to note, (...) that such innovations are actually being introduced, not merely in minor details but in matters of major importance as well. They are, in point of fact, those who make use of the vernacular in the celebration of the august Eucharistic Sacrifice; those who transfer certain feast days � which have been appointed and established after mature deliberation � to other dates; those finally who delete from the prayer books approved for public use the sacred texts of the Old Testament, deeming them little suited and inopportune for modern times.

The use of the Latin language, customary in a considerable portion of the Church, is a manifest and beautiful sign of unity, as well as an effective antidote for any corruption of doctrinal truth." (Pius XII: Encyclical Mediator Dei, November 20, 1947)