“The more one longs for a thing, the more painful does deprivation of it become. And because after this life, the desire for God, the Supreme Good, is intense in the souls of the just (because this impetus toward Him is not hampered by the weight of the body, and that time of enjoyment of the Perfect Good would have come) had there been no obstacle; the soul suffers enormously from the delay.”
—St. Thomas Aquinas

I do not think that apart from the felicity of Heaven, there can be a joy comparable to that experienced by the souls in Purgatory. An incessant communication from God renders their joy more vivid from day to day: and this communication becomes more and more intimate, to the extent that it consumes the obstacles still existing in the soul….On the other hand, they endure pain so intense, that no tongue is able to describe it. Nor is any mind capable of comprehending the smallest spark of that consuming fire, unless God should show it to him by a special grace.
— Saint Catherine of Siena

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Hostias et preces tibi, Domine, laudis offerimus.
Tu suscipe pro animabus illis, quarum hodie
memoriam facimus,
fac eas, Domine,
de morte transire ad vitam quam olim Abrahae promisisti et semini ejus.

We offer Thee, O Lord,
sacrifices and prayers of praise;
do Thou accept them for those souls
whom we this day commemorate;
grant them, O Lord,
to pass from death to the life which Thou once didst promise
to Abraham and his seed.

Second half of the Offertory of the Requiem Mass