You were sent to heal the contrite of heart:Ps 147:3; Isa 57:15; 61:1These petitions originated as embellishments to the Kyrie in its various musical settings.
Lord, have mercy. (Kyrie, eleison.)Ps 123:3; Mt 20:31; Lk 17:13
You came to call sinners:Matt. 9:13; 1 Tm 1:15
Christ, have mercy. (Christe, eleison.)1 Tm 1:2; Jude 21
You are seated at the right hand of the FatherEph 1:20; Col 3:1; Heb 1:3
to intercede for us:Rom 8:34; Heb 7:25
Lord, have mercy. (Kyrie, eleison.)
All three petitions are specifically related to sin and forgiveness. The first evokes Isaiah 61:1, some of which Jesus read in the synagogue at His hometown of Nazareth: “The Spirit of the Lord GOD is upon me … to bind up the brokenhearted.” The second comes from St. Matthew’s Gospel where he records the Lord’s call to him, a tax collector: “I came not to call the righteous, but sinners.” (Mt 9:13) The third comes from St. Paul’s letter to the Romans where he says that Christ “is at the right hand of God, [where he] indeed intercedes for us.” (Rom 8:34)
The petitions in general describe what our Lord has done, is doing, or will do, as if the priest were saying, “Lord, sent to heal the contrite of heart, have mercy.” Christ came for us sinners, but forgiveness requires contrition on our part, and His work on our behalf continues in Heaven, “since he always lives to make intercession for [us].” (Heb 7:25) This is why, even after being baptized into Christ, we still require forgiveness of our sins and confess them. Our Catholic identity calls us to continual conversion and contrition for our sins, lest we harden our hearts and lose our salvation through mortal sin.
Forms A and B of the Penitential Act are followed by the Kyrie (without petitions); Form C is not followed by the Kyrie because it incorporates it.