Just about every Catholic and Orthodox Christian is very familiar with the triple litany: “Lord, have mercy; Christ, have mercy; Lord, have mercy.” This text has been a very standard phrase at Mass in the Eastern Churches since the fourth century, and was incorporated into the Eucharistic celebration in our Western Church in the ninth century. As a sign of its origins in the East we still rather frequently pray the words in ancient Greek: “Kyrie eleison; Christe eleison; Kyrie eleison.”
Many people are surprised to find out that this triple litany is not primarily a penitential phrase, although it does appear to beg God’s forgiveness. It rather is a statement of utter dependence upon God, a phrase that acknowledges God (whether Father, Son, or Spirit) as superior to ourselves. For this reason, the short invocations that sometimes are used in conjunction with the Litany are supposed to highlight God’s distinctive deeds and superiority, not human sinfulness.
For example, “You are Mighty God and Prince of Peace” is a very popular, standard invocation just prior to “Lord, have mercy.” Notice how it’s not really a call for forgiveness? Instead, it’s a humble acknowledgement of God’s pre-eminence, and of course of our own corresponding lowliness.