About twenty years ago I studied Koine Greek in college and learned the so-called Erasmian pronunciation of it. It always sounded ugly and artificial to me, but that's just my personal opinion. It just didn't sound like a real living language. I found it lacked musicality, flow, and beauty. It just didn't sound "alive."
Then I converted to Orthodoxy fifteen years ago. I converted in a parish with Russian Orthodox roots that used mostly English for its liturgies. The most we used Church Slavonic was maybe once a month at best, usually a Saturday morning Liturgy for our families from Russia and Eastern Europe. Sometimes we still have moliebens on Sunday afternoons in Slavonic. I cannot read the Cyrillic alphabet. I've never had any formal instruction in Russian or Church Slavonic, and I don't know any other Slavic languages. However, I do seem to have an aptitude for foreign languages. I learned both French and German with ease and am fairly competent in both of them. However, in the 15 years I have been in the Russian Orthodox Church, I know EXACTLY where I am in a Slavonic Liturgy. I don't understand every word of course. But here is a short list of things I do recognize and understand in Slavonic:
1. Blessed is the Kingdom ...
2. Lord, have mercy
3. Grant this, O Lord
4. The Trisagion Hymn
5. The Creed
6. The Our Father
7. Bless the Lord, O my soul
8. The Paschal Troparion
9. Glory to God in the highest
10. O Heavenly King
11. The Sanctus
12. The Jesus Prayer
13. Rejoice O Virgin, Theotokos
I find Slavonic to be a rich, beautiful and melodious sounding language. I like it, although I do prefer to attend English liturgies since English is my native language. I am not critical of the Russian Orthodox Church for worshiping in Slavonic instead of contemporary Russian. One thing I decided to do long ago when I converted was not to become a "know-it-all" convert. I respect the Mother Church and in my case, the Church of Russia is my Mother Church. If the mother Church wants to keep Slavonic, that's her business, not mine. It isn't my place as a mere convert to lecture the Mother Church on what she should do. That's for the bishops and pastors of the Russian Church to decide on their own in how to best meet the spiritual needs of their people.
I once visited a Greek Orthodox monastery where the Abbot told me the following story about Koine Greek. I will repeat it here for those of you who may have never heard this explanation:
Koine Greek and how to pronunce it (according to Father Nicholas):
Koine Greek was invented by the scholars of Alexander the Great as a simplified way of speaking the Greek language. The reason that they invented it was because until that time, Greeks only spoke local dialects of the Greek language. Greeks from different areas of Greece could not understand each other without a lot of difficulty. The Greeks from Athens could not understand the people from Sparta or Thessaloniki or the Islands easily. The dialects really hampered their ability to communicate. So Alexander's scholars developed Koine or "Common" Greek, creating a language from the common Greek vocabulary that all people who spoke Greek could understand. They tried to edit out regional dialects and local variations from the language and they simplified a lot of the grammatical structure that Classical Greek has. This new language of Koine Greek was a great success. Not only did the Greeks like it, it spread throughout the entire Levant as a language of trade and communication. In fact, it probably became the world's first international language. Because of a vowel shift that occurred around 300 B.C. or so, Koine Greek is not pronounced in the same manner as Classical Greek. This is most noticeable with the Greek letters oi in classical Greek. Although Koine Greek retains a lot of the Classical Greek spelling, it simplified these Classical Greek pronunciations so that the Classical oi sound is replaced with just the i sound, even though the Koine word is still written with the oi.
Father Nicholas stressed that the Ecclesiastical Greek used by the Greek Orthodox Church today uses this inherited Koine Greek pronunciation. This is not the Demotic Greek language used for sermons and announcements. I am talking here about Koine Greek used in the liturgy. Father Nicholas went on further to say that the so-called pronunciation of Erasmus taught in most American and Western European universities is a modernist reconstruction at best. What the Erasmian pronunciation does is try to reconstruct what Classical Greek might have sounded like: The Greek of Plato and Aristotle. The problem is, Koine Greek is not the Greek of Plato and Aristotle. Koine Greek is the Greek of Alexander the Great, the New Testament and the Early Church. It is far removed from Classical Greek. And Koine Greek already has its own proper pronunciation: The Church has been using this pronunciation for the past 2,000 years. It is called the "Received Pronunciation" or Ecclesiastical Greek. It is the Greek of the Greek Orthodox Church. It is indeed quite foolish to try to impose an Erasmian pronunciation on Koine Greek! Think of the hubris in that! Erasmus never even visited Greece. He never got to hear the Greek language as a living, breathing thing spoken by real Greeks. And Erasmus is going to correct the pronunciation of the Church? A language that the Church was using for over 1,500 years before Erasmus was ever born? It is not the case that Greeks pronounce Koine Greek like Modern Greek (Demotic). The actually case is the reverse. Demotic Greek is pronounced in the same manner as Koine Greek. That's the point Westerners and the non-Orthodox often don't understand or refuse to understand.
I hope these words have shed some light on this topic.