Treatise On Purgatory - Separation from God is the greatest pain

Separation from God is the greatest pain of purgatory. In this, purgatory differs from hell.

“The source of all suffering is either original or actual sin. God created the soul pure, simple, free from every stain, and with a certain beatific instinct toward himself. It is drawn aside from aim by original sin, and when actual sin is afterwards added, this withdraws it still farther, and ever as it removes from him its sinfulness increases because its communication with God grows less and less. “And because there is no good except by participation with God, who, to the irrational creatures imparts himself as he wills and in accordance with his divine decree, and never withdraws from them, but to the rational soul he imparts himself more or less, according as he finds her more or less freed from the hindrances of sin, it follows that, when he finds a soul that is returning to the purity and simplicity in which she was created, he increased in her the beatific instinct, and kindles in her a fire of charity so powerful and vehement, that it is insupportable to the soul to find any obstacle between her and her end; and the clearer vision she has of these obstacles the greater is her pain. “Since the souls in purgatory are freed from the guilt of sin, there is no barrier between them and God save only the pains they suffer, which delay the satisfaction of their desire. And when they see how serious is even the slightest hindrance, which the necessity of justice causes to check them, a vehement flame kindles within them, which is like that of hell. They feel no guilt however, and it is guilt which is the cause of the malignant will of the condemned in hell, to whom God does not communicate his goodness, and thus they remain in despair and with a will forever opposed to the good will of God.