Purgatory exists because God is both just and merciful.
Purgatory is “like a refiner’s fire” (Mal 3:2). It refines and purifies those who at the moment of death are neither good enough for an immediate heaven or bad enough for hell.
CCC1030 All who die in God’s grace and friendship, but still imperfectly purified, are indeed assured of their eternal salvation; but after death they undergo purification, so as to achieve the holiness necessary to enter the joy of heaven.
CCC1031 The Church gives the name Purgatory to this final purification of the elect, which is entirely different from the punishment of the damned. The Church formulated her doctrine of faith on Purgatory especially at the Councils of Florence and Trent. The tradition of the Church, by reference to certain texts of Scripture, speaks of a cleansing fire:
As for certain lesser faults, we must believe that, before the Final Judgment, there is a purifying fire. He who is truth says that whoever utters blasphemy against the Holy Spirit will be pardoned neither in this age nor in the age to come. From this sentence we understand that certain offenses can be forgiven in this age, but certain others in the age to come.
The existence of purgatory logically follows from two facts: our imperfection on earth and our perfection in heaven.
At the moment of death, most of us are not completely sanctified (purified, made holy), even though we are justified, or saved by having been baptized into Christ’s Body and having thereby received God’s supernatural life into our souls, having accepted him by faith and not having rejected him by unrepented mortal sin.
……but in heaven we will be perfectly sanctified, with no lingering bad habits or imperfections in our souls.
Therefore, for most of us, there must be some additional change, some purification, between death and heaven. This is purgatory.
Is purgatory found in Scripture? You decide:
Scripture speaks of a cleansing spiritual fire: (1 Cor 3:15, 1 Pet 1:7)
In death many of us are still imperfect: (1 Jn 1:8 )
In heaven we will all be perfect: (Mt 5:48, Rev 21:27)
Scripture also distinguishes sins that cannot be forgiven either before or after death from sins that can be forgiven after death: (Mt 12:31-32)
The reality of purgatory is found in Scripture, though not the word – just like the Trinity.