That prayer has great power

Which a person undertakes with all his might.
It makes a bitter heart sweet
A sad heart happy
A poor heart rich
A foolish heart wise
A faltering heart bold
A weak heart strong
A blind heart seeing
A cold soul burning.
It draws great God down into a small heart.
It drives the hungry soul up to God’s fullness.
It brings together two lovers, God and the soul, to a place of bliss.
There they talk much of love.
O woe! That I, unhappy sack of misery, cannot die there!

A despondent person asked me to pray for him, which I did with fear and special concern. God heard me with his gaze, with his words, and with his true voice, saying: “There is no lamb so white or so pure that it cannot be vanquished by wolves; yet no one can deter my determinations. I have made this clear to him in three ways. First, I was merciful in regard to his guilt. Second, I have given him my grace. Third, I have never allowed untrustworthy people to exercise any power over him.”

Then I lamented for him thus: “Lord, he still has great fears that you have not completely forgiven him his guilt.”

Thus did God reply: “That would be impossible. Whoever is sorry for his sins I forgive. Those who repent with deep compunction I grant my grace; and whoever so repents them that he would sacrifice his life before he would ever do it again and remains constant in this shall not be condemned to any punishment after this life because of his guilt, unless he commits real venial sins and is found unrepentant of them.”

On the last day, Christ Jesus shall hold aloft a glorious scale before his father. Upon it will lie his holy toil and his innocent suffering, and in it and next to it all the blameless torment, humiliation, and interior pain that was ever suffered by human beings for the love of Christ. Indeed, when the right side of the scales sinks, those rejoice the most who have much upon it.

Source: Mechthild of Magdeburg, The Flowing Light of the Godhead, trans. Frank Tobin (Paulist Press, 1998), 149–150, 181, 191.