“Eternal rest grant unto them, O Lord.
And let perpetual light shine upon them.”
There is no joy save that in paradise to be compared with the joy of the souls in purgatory. As the rust of sin is consumed, the soul is more and more open to God's love. Just as a covered object left out in the sun cannot be penetrated by the sun's rays, in the same way, once the covering of the soul is removed, the soul opens itself fully to the rays of the sun.
Having become one with God's will, these souls, to the extent that he grants it to them, see into God. Joy in God, oneness with him, is the end of these souls, an instinct implanted in them at their creation.
All that I have said is as nothing compared to what I feel within, the witnessed correspondence of love between God and the soul; for when God sees the soul pure as it was in its origins, he tugs at it with a glance, draws it and binds it to himself with a fiery love.
God so transforms the soul in himself that it knows nothing other than God. He will not cease until he has brought the soul to perfection. That is why the soul seeks to cast off any and all impediments, so that it can be lifted up to God; and such impediments are the cause of the suffering of the souls in purgatory. Not that the souls dwell on their suffering; they dwell, rather, on the resistance they feel in themselves against the will of God, against his intense and pure love bent on nothing but drawing them up to him.
And I see rays of lightning darting from that divine love to the creature, so intense and fiery as to annihilate not the body alone but, were it possible, the soul. The soul becomes like gold that becomes purer as it is fired, all dross being cast out.
The last stage of love is that which does it work without human doing. If humans were to be aware of the many hidden flaws in them, they would despair. These flaws are burned away in the last stage of love. God then shows the soul its weakness, so that the soul may see the workings of God.
If we are to become perfect, change must be brought about in us and without us; that is, change is to be the work not of human beings but of God. This, the last stage of love, is the pure and intense love of God alone.
The overwhelming love of God gives the soul a joy beyond words. In purgatory great joy and great suffering do not exclude one another.
St. Catherine of Genoa
Purgation and Purgatory