For souls burdened with the memory of their sins
From the Novena for the Holy Souls in Purgatory
Sacred Scripture: Psalm 51:3-4
Meditation for Day 3
In Purgatory, the holy souls see with piercing clarity the full ugliness of every sin committed against God — a vision far more painful than any earthly remorse. The Psalmist's cry becomes their own: For I know my transgressions, and my sin is ever before me. Against you, you only, have I sinned and done what is evil in your sight (Ps 51:3-4). Yet this painful awareness is also purifying, burning away the last attachments that prevented union with God. We pray today for those souls who carry the heaviest burden of regret, trusting in God's infinite mercy that their suffering will end in everlasting joy.
Daily Novena Prayer (recited every day)
Closing Prayer
O God, the author of mercy, the lover of the salvation of mankind; we address thy clemency, in behalf of our brethren, relations, and benefactors, who are departed this life, that by the intercession of blessed Mary, ever virgin, and of all the saints, thou wouldst receive them into the enjoyment of eternal happiness; through Christ our Lord. Amen.
Concluding prayers: Many novena traditions add one Our Father, one Hail Mary, and one Glory Be at the close of each day's prayer.
Source
https://www.ewtn.com/catholicism/devotions/novena-for-the-holy-souls-in-purgatory-286