(2.42) The Penitential Act (Second and Third Form)
The Second Form of the Penitential Act is an exchange between the Priest and the Assembly:
Priest says: Have mercy on us, Lord
We say: For we have sinned against you.
Priest says: Show us, O Lord, your mercy
We say: And grant us your salvation
The passages are found on the Prayer for the Restoration of God's Favor: "Show us your steadfast love, O Lord, and grant us your salvation" (Psalm 85:7)
The Third Form of the Penitential Act is a three-fold act of praising the Lord and asking for his mercy. This follows a three-fold pattern of many rituals in our mass and especially our prayers on the Father, the Son and the Holy Spirit.
Priest says:
You were sent to heal the contrite of heart: Lord, have mercy
We say:
Lord, have mercy.
Priest says:
You came to call the sinners: Christ, have mercy.
We say:
Christ, have mercy.
Priest says:
You are seated at the right hand of the Father to intercede for us: Lord, have mercy.
We say:
Lord, have mercy.