One of my Classmates asked me today about why we can't just use the vulgar during the liturgy, well he didn't quite put it that way he said vernacular but it is the same thing. The vernacular is the common tongue and vulgar simply means common. But I will deal with vulgarity in the worship of The Supreme Being and Creator of the Universe in another part of this post, for now let me deal with why we use Latin to begin with.
Hebrews 9:1-9 tells us that in the Temple a veil separated the Holy of Holies where God dwelt from the rest of the Temple where men dwelt. This signified that man was separated from God by sin (Isaiah 59:1-2). Only the High Priest was permitted to pass beyond this veil once each year (Exodus 30:10; Hebrews 9:7), enter into God's presence for all of Israel, and make atonement for their sins (Leviticus 16).
It was the practice of the early Christians to place between the celebrant and those in attendance a veil which bot thinner and thiner in the Wester Latin Rite church. We can still see evidence of this veil however in the Western Churches in what is commonly known as an Iconostasis. This wall which separates the sanctuary from the common of the Church. We don't today think much of that word sanctuary so let me make this point about it sanct-u-ary, SAiNct, SAiNT, sanctus in latin means Holy the sanctuary is the Holy place, while the entire church is Holy the Sanctuary is the Holy of Holies just like the temple was Holy and the temple had a special Holy of Holies(Sanctuary) where God dwelled. For this reason the Early Christians believing in the Body Blood Soul and Divinity of Iesus Christ in the Eucharist divided the place where the sacrament was consecrated and the people. The Iconostasis which is still used today in the East both Eastern Orthodox and Eastern Catholic maintains a thin veil and doors that are shut and opened several times during the Liturgy. In the Latin Church though because of many different factors the veil was replaced by Latin.
As I heard a Priest once say "Be the mass in English or in Latin we do not understand what is going on, it is a mystery." Only in the most inferior way do I in no language understand what is going on because language cannot express a mystery. If you were to say to me "I can explain to you in clear Language "This is my body, This is my blood" I would call you a liar, it simply is not possible, Transubstantiation does not explain how the bread and wine become the body and blood of Christ only that it does and what we cannot say about the concerted bread and wine. I cannot understand how Iesus comes down and becomes the bread and wine or rather transforms them into him and how they maintain their attributes while not at all being bread and wine or while being bread and wine but not. Does your head hurt yet? Good you are just now beginning to understand what I mean about not understand. I will stop explaining about how you cant understand before your head explodes.
This is one reason we use Latin to help express the mystery. However that is not the only reason take again the Jewish and the and our Jewish roots, we are Jeudao-Christians or Jewish-Christians as opposed to Gnostic-Christians. The Jews had the practice at least in the time of Christ spoke Aramaic and Hebrew, Hebrew was reserved for the temple and Liturgical celebrations. In the same tradition we use two languages for our Liturgical tradition because the Vulgar the common is unfit for God, thus we have a special language to express the sacredness of God. We set apart certain cloths and certain symbols for the medical instruments of God(doctor), Bishops (the stethoscope), Priests (the scalpel), Deacons(tongue supressor), Religious brothers and sisters(penlight). So in the same way Peoples have been set aside as the special property of God we too set a language aside as a special tongue by which to communicate to God thus Latin is a Holy language just as Greek and Hebrew are Holy or Sanctified Languages. This Language now removes the Veil while still dividing the vulgar from the Holy, It creates an invisible shield for the Holy of Holies. Just as it is fitting and proper for us to not wear vulgar cloths to church so it is fitting and proper to speak a special tongue.