These particular words express a plea for the full richness of God's mercy within our vulnerability.
Within the Roman Rite Latin is the official language of the Mass, which is then normally translated into the vernacular. However, one phrase within the liturgy stands out from the rest because the words are not Latin, but Greek.
During the penitential rite at the beginning of Mass the priest or deacon will sometimes say, or the cantor sing, “Kyrie eleison” (“Lord, have mercy”): Greek words that were never converted into Latin. Why is that?
First of all, according to the Catholic Encyclopedia, “It is certain that the liturgy at Rome was at one time said in Greek (to the end of the second century apparently).” In this regard the Greek words remind us of our Greek origins. Besides the Mass, the New Testament was originally written in Greek and the apostles frequently evangelized Greek-speaking Jews and Gentiles. In fact, the Divine Liturgy of the Eastern Churches, which maintain the ancient forms, incorporate the phrase “Kyrie eleison, or its equivalent in Slavonic or other languages, in many places throughout the Mass. It is a common response to litanies, as we hear when we pray the Litany of the Saints at the Easter Vigil.
Some scholars, however, believe the words “Kyrie eleison” were not a remnant of the Greek, but were added centuries later into the Roman Rite. This means the inclusion of the Greek words in the Latin Mass was deliberate and significant.
It is believed that the primary reason why the phrase “Kyrie eleison” wasn’t translated into Latin is that the words would have lost their original meaning. The book Orthodox Worship describes the true meaning of the phrase.
“The word mercy in English is the translation of the Greek word eleos. This word has the same ultimate root as the old Greek word for oil, or more precisely, olive oil; a substance which was used extensively as a soothing agent for bruises and minor wounds. The oil was poured onto the wound and gently massaged in, thus soothing, comforting and making whole the injured part. The Hebrew word which is also translated as eleos and mercy is hesed, and means steadfast love. The Greek words for ‘Lord, have mercy,’ are ‘Kyrie, eleison’ that is to say, ‘Lord, soothe me, comfort me, take away my pain, show me your steadfast love.’ Thus mercy does not refer so much to justice or acquittal a very Western interpretation but to the infinite loving-kindness of God, and his compassion for his suffering children! It is in this sense that we pray ‘Lord, have mercy,’ with great frequency throughout the Divine Liturgy.”
In light of this explanation the phrase comes alive and highlights the beauty and depth of God’s mercy. It shows a loving God who wants to bind our wounds like the Divine Physician he is. Instead of standing in front of a tribunal at the beginning of Mass asking for mercy from a powerful judge, we are face-to-face with a compassionate God, who is ready to pick us up when we fall down.
So while it may seem strange to speak Greek words at Mass, the Church chose those words centuries ago specifically for their deep and powerful meaning.