The existence of Purgatory is so certain that no Catholic has ever entertained a doubt of it. It was taught from the earliest days of the Church and was accepted with undoubting faith wherever the Gospel was preached. The doctrine is revealed in Holy Scripture, and has been handed down by Tradition, taught by the infallible Church and believed by the millions and millions of faithful of all times. 

Only those souls that are completely free of sin can enter heaven. It stands to reason, then, that the soul with unforgiven sins or the souls of those who have not yet atoned for their sins during their lifetime, yet tried to live as God would have us live, cannot enter Heaven and do not deserve Hell.

Purgatory, then, is a place of temporal punishment for those who die in God's grace, but are not entirely free from venial sins or have not entirely paid the satisfaction due to their sins. The existence of purgatory is universally taught by all the Fathers of Church. The words of OurLord , "Thou shalt not come out from it until thou hast paid the last penny" are very clear (Matt. 5 :25) Later, when speaking of the sins againt the Holy Spirit, Jesus says such a sin "will not be forgiven either in this world or in the next," implying that there are some sins that cannot be atoned for in this world (Matt. 12:32). 

Saint Paul shows his belief in purgatory when, in his second letter to Timothy he prays for the deceased Onesiphorus. "May the Lord grant him to mercy from the Lord on that day. (2 Tim. 1 :18). Even in the Old Testament there was a belief in the existance of purgatory, for there we find Judas Machabeus sending 12,000 drachmas to Jerusalem to have sacrifiices offered for the sins of the dead. That chapter ends with the advice: "It is therefore a holy and wholesome thought to pray for the dead, that they may be loosed from sins" (2 Mach. 12 :46).

In purgatory, souls suffer for a while in satisfaction for their sins before they can enter heaven. The principal suffering of these souls consists in the pain of experiencing, on the one hand, an intense longing for God and, on the other, a realisation that they are hindered from possessing Him by reason of their past sins. Unlike the souls in hell, they are certain of one day seeing God. They can be helped, moreover, by the prayers of the faithful on earth, and especially by the offering of Mass.

In the "Decree on Purgatory," we read, "The Catholic Church, instructed by the Holy Spirit and in accordance with Sacred Scripture and the ancient Tradition of the Fathers, has taught in the holy Councils and most recently in this ecumenical Council that there is a purgatory, and that the souls detained there are helped by the acts of intercession ... of the faithful and especially by the acceptable Sacrifice of the altar" (Council of Trent,1563).

Padre Pio had a very special relationship with the Holy Souls..indeed such was the relationship that they were his frequent visitors..and led him to say: "I see so many souls from Purgatory that they don't frighten me any more. More souls of the dead than the living climb this mountain to attend my Masses and seek my prayers."

When Padre Pio was asked how long a particular soul would stay in Purgatory he replied "At least one hundred years. We must pray for the Souls in Purgatory. It is unbelievable, what they can do for our spiritual good, out of gratitude they have towards those on earth who remember to pray for them."

The length of time souls are detained in Purgatory depends on:
📨 The number of their faults;  
📨 On the malice and deliberation with which these have been committed;  
📨 On the penance done, or not done, the satisfaction made, or not made for sins during life;  
📨 Much, too, depend on the suffrages offered for them after death by friends and relatives still alive. 

What can be safely said is that the time souls spend in Purgatory, as a rule, is very much longer than people commonly imagine.

The Doctrine Of Purgatory
Fr. Hardon gives a thorough explanation of the Doctrine of Purgatory, including contrary views, biblical references, and quotes from the fathers on purgatory.

How To Argue the Existence of Purgatory
A defense of purgatory, including consideration of prayers for the dead and the sufficiency of Christ's sacrifice.

A Most Reasonable Doctrine
Fr. Buckley offers an explanation of the doctrine of Purgatory, how to atone for sins, and how to gain indulgences for the dead.

Praying for the Dead and Gaining Indulgences During November
A short article explaining indulgences and practices we can do during the month of November for the Poor Souls in Purgatory.

 Purgatory: Service Shop for Heaven
In this article Fr. Anthony Zimmerman spells out the Catholic doctrine about Purgatory.