Kyrie eleison.
Kyrie eleison.
Christe eleison. "Christ, have mercy."
Christe eleison.
Christe eleison.
Kyrie eleison. "Lord, have mercy"
Kyrie eleison.
Kyrie eleison.

Using the Greek words for 'Lord' and 'Christ' the priest and the servers ask God (on behalf of themselves and all present) for mercy, in three sets of three prayers.
In the three-fold repetition we implore mercy from God in His three persons. We also reflect on the need to be persistant in prayer. In Luke 18:35 we read,

"Now it came to pass, when he drew nigh to Jericho, that a certain blind man sat by the way side, begging. 36 And when he heard the multitude passing by, he asked what this meant. 37 And they told him, that Jesus of Nazareth was passing by. 38 And he cried out, saying: Jesus, son of David, have mercy on me. 39 And they that went before, rebuked him, that he should hold his peace: but he cried out much more: Son of David, have mercy on me. 40 And Jesus standing, commanded him to be brought unto him. And when he was come near, he asked him, 41 Saying: What wilt thou that I do to thee? But he said: Lord, that I may see. 42 And Jesus said to him: Receive thy sight: thy faith hath made thee whole. 43 And immediately he saw, and followed him, glorifying God. And all the people, when they saw it, gave praise to God.

The repetition of these prayers recalls the persistance of the blind beggar, who, when his prayer was not immediately answered, called out all the louder, "Son of David, Have mercy on me". This passage shows that God does not always answer our prayers on the first try. Sometimes he requires that we be persistant. but he also teaches that if we ask it will be granted and if we knock it will be opened unto us. so we must persist in prayer and not give up if our prayers are not answered immediately. God in His wisdom knows better than we, what is for our good.