The following is taken from THE CATECHISM EXPLAINED Spirago - Clarke 1899.
Latin is well adapted for the services of the Church, because it is both venerable and mysterious. It is venerable on account of its origin and its antiquity; it is the language in which the praises of God resounded from the lips of Christians during the first centuries. It is a sublime and solemn thought that the holy sacrifice is now offered in the same language, nay, with the very same words as it was offered in times long past in the obscurity of the Catacombs. There is also an element of mystery about the Latin tongue; it is a dead language, not understood by the people. The use of an unknown tongue conveys to the mind of the vulgar that something is going on upon the altar which is past their comprehension, that a mystery is being enacted. In the first centuries of Christianity a curtain used to be drawn during the time from the Sanctus to the communion, to conceal the altar from the sight of the worshippers. This is now no longer done, but the use of an unknown tongue has something of the same effect, by inspiring the awe into the minds of the common people. It is a striking fact that Israelites and pagans made use, in the worship of the Deity, of a language with which the multitude were not conversant. The Israelites made use of the ancient Hebrew, the language of the patriarchs; we do not find Our Lord or the apostles censuring this practice. The Greek Church, both orthodox and schismatic, employs the old form of the Greek language for divine service, not that spoken at present. The same language is in use in the Russian (so-called orthodox) Church, not the vernacular, which is a Slavonic dialect.
The use of Latin is a means of maintaining unity in the Church, as well as uniformity in her services. for the use of one and the same language in Catholic churches all over the surface of the globe, is a connecting link binding them to Rome, and making one nations which are separated by diversity of tongues. Latin, as the language of the Church, unites all nations, making them members of God's family, of Christ's kingdom. The altar on earth is a type of the heavenly Jerusalem where a great multitude of all peoples and tongues stand around the throne, praising God. If Latin were not the official language of the Church, deliberations and discussions among bishops assembled at the councils, the mutual exchange of opinions between theologians would be impossible. Moreover, the use of Latin, the language of ancient Rome, is a constant reminder of our dependence on the Holy Roman Church; it recalls to our minds involuntarily the fact that thence, from the Mother Church, the first missionaries came who brought the faith to our shores. The use of a dead language is a safeguard against many evils; it is not subject to change, but remains the same to all time. Languages in daily use undergo a continual process of change; words drop out, or their meaning is altered as years go on. If a living language were employed in divine worship heresies and errors would inevitably creep into the Church, and sacred words would be employed in an irreverent or mocking manner by the unbeliever. This is prevented by the use of Latin, at any rate as far as the unlearned are concerned.
Yet the Church is far from desiring to keep the people in ignorance of the meaning of her religious services; the decrees of the Council of Trent (22, 8), strictly enjoin upon priests to explain frequently the mysteries and ceremonies of the Mass to the children in schools, and to adults from the pulpit. But as a matter of fact, it is by no means necessary for the people to understand every detail of the ceremonial of the Mass. "If," says St. Augustine, "there are some present who do not understand what is being said or sung, they know at least that all is said and sung to the glory of God, and that is sufficient for them to join in it devoutly." Moreover, experience teaches that the fact of the prayers being in Latin does not at all hamper or interfere with the devotion of the faithful, or lead them to absent themselves from the services of the Church. Besides, the sermons are always delivered in the vernacular; it is often used at the opening services and to some extent in administering the sacraments. The reason why the whole of the Mass is in Latin is because it is a sacrifice, not an instruction for the people, The greater part of the prayers are said by the priest secretly, so that were they in the mother tongue, they would be inaudible to the people. Furthermore, the celebration of Mass consists more in action than in words. The actions of the priest, the whole ceremonial, speaks a language intelligible to all. And if, as some would wish, all the services were conducted in the language of the country, persons of another nationality, not conversant with other languages, might be led to drop their religion on leaving their own land.
Another evil consequent upon such a change would be a lessening of the respect felt for the holy sacrifice, as was proved at the time of the reformation, when the prayers of the Mass were, to a great extent, translated into German and English.