In purgatory, the more the soul is consumed, the more it exposes itself to God

"I don't believe there can be found a comparable contentment to that of a soul in purgatory, if you except the saints that are in heaven. Each day this contentment increases through God's action in those souls, and this action keeps augmenting at the same time as all that impedes this divine action burns away. This impediment is the rust of sin. Fire slowly consumes this rust and thus the soul exposes itself more and more to the divine influx.

Just like an object shrouded by something cannot respond to the radiance of the sun - not because the sun is insufficient since it keeps on shining but because of the impediment caused by what is wrapping the object. If the obstacle that acts as a screen is burnt away, the object will expose itself to the action of the sun; it will experience this action in proportion to the diminution of the obstacle. Thus the rust of sin is what shrouds the soul.

In purgatory this rust is consumed by fire. The more it is consumed, the more the soul exposes itself to the true sun which is God. Its joy increases as the rust disappears and the soul is exposed to the divine ray of sun. Thus the one increases and the other diminishes until the time is accomplished. Suffering isn't what diminishes, only the time to spend in that pain becomes shorter.

The souls that are in purgatory find themselves without the guilt of sin. Consequently, there is no obstacle between God and them besides this suffering that hinders them and consists in that their beatific instinct hasn't reached its full perfection."

-- Treatise on Purgatory by St Catherine of Genoa