In the Tridentine Mass the Kyrie is recited by the priest alternating with the server(s) in the nine-fold Kyrie. From the Catholic Encyclopedia: “So we have, at least from the eighth century, our present practice of singing immediately after the Introit three times Kyrie Eleison, three times Christe Eleison, three times Kyrie Eleison, making nine invocations altogether. Obviously the first group is addressed to God the Father, the second to God the Son, the third to God the Holy Ghost.”
No matter how much we love our Lord, let us remember that when left to our own weakness, we too, will deny Him. Let us heed our Lord’s admonishment to “watch and pray that ye enter not into temptation.” We place all our hopes in the mercy of the Triune God.
“Lord Jesus Christ who didst suffer Thyself to be thrice denied by the Prince of Thy Apostles in the house of Caiphas, preserve me, I bessech Thee, from ill company that I may suffer all worldy losses, and even death itself, rather than deny Thee once. Amen.”
In the N.O. the Kyrie may be led by the priest, or a song leader, in a six-fold Kyrie. It may be done following the Penitential rite, or alone as one of the options in that rite.