Dear Michael:

For the purposes of our readers, I will start with a definition of purgatory. We learn what is essentially a dictionary definition of purgatory in 1 Corinthian 3:12-15~

12 If anyone builds on this foundation using gold, silver, costly stones, wood, hay or straw, 13 their work will be shown for what it is, because the Day will bring it to light. It will be revealed with fire, and the fire will test the quality of each person’s work. 14 If what has been built survives, the builder will receive a reward. 15 If it is burned up, the builder will suffer loss but yet will be saved—even though only as one escaping through the flames.

Everyone in purgatory will be in heaven, but they must be purge of the residue of sin and bad things they did, the consequences of sin in this life. As St. Paul says here, "If it is burned up, the builder will suffer loss but yet will be saved—even though only as one escaping through the flames".

Contrary to what some Protestant denominations believe, when one dies in the friendship of God (the person is saved and will go to heaven), that salvation does not mean the person is fully holy yet, fully sanctified.

Purgatory purges those defects of saved people before entering the throne room of God. One cannot go before God with any blemishes. In a way purgatory is taking a shower before meeting our Lord. This is a shower of fire that will burn up the wood, hay and straw in our lives.

While good works do not get us to heaven (Romans 3:28), if we are truly saved then our faith will produce works of love. If our faith does not do that, then we have no faith. If we have no faith, we have no salvation. (James 2:14-26)

Most of us will have good works and not so good works in our life. It is the not so good works, the (wood, hay, straw) that must be purged from us before entering heaven before the beatific vision.

Purgatory is a great gift from God because He knows we are not perfect. Thus, He has provided this means to prepare us for perfection so that we may see Him in His beatific vision.

The Modern Catholic Dictionary defines purgatory as:

PURGATORY. The place or condition in which the souls of the just are purified after death and before they can enter heaven. They may be purified of the guilt of their venial sins, as in this life, by an act of contrition deriving from charity and performed with the help of grace. This sorrow does not, however, affect the punishment for sins, because in the next world there is no longer any possibility of merit. The souls are certainly purified by atoning for the temporal punishments due to sin by their willing acceptance of suffering imposed by God. The sufferings in purgatory are not the same for all, but proportioned to each person's degree of sinfulness. Moreover, these sufferings can be lessened in duration and intensity through the prayers and good works of the faithful on earth. Nor are the pains incompatible with great peace and joy, since the poor souls deeply love God and are sure they will reach heaven. As members of the Church Suffering, the souls in purgatory can intercede for the persons on earth, who are therefore encouraged to invoke their aid. Purgatory will not continue after the general judgment, but its duration for any particular soul continues until it is free from all guilt and punishment. Immediately on purification the soul is assumed into heaven. (Etym. Latin purgatio, cleansing, purifying.)

Also see, The Roots of Purgatory.

Now to your questions:

It is not only Christians who may spend time in purgatory. Anyone to whom God chooses to save will likely spend time in purgatory also. Nothing unclean can go before our Lord, thus all those saved and going to heaven must be cleansed either in this life, or in purgatory.

It is true that in the spiritual world (the afterlife) the laws of time and space do not exist. For those in purgatory the time spent there may seem to be 10 years as we recon time, we to them it may be only a second. This is why the Church stopped reference to actual times for indulgences (e.g. 200 years reduced in purgatory) and now just refers to plenary and partial indulgences.

Catechism of the Catholic Church, which states:

"An indulgence is obtained through the Church who, by virtue of the power of binding and loosing granted her by Christ Jesus, intervenes in favor of individual Christians and opens for them the treasury of the merits of Christ and the saints to obtain from the Father of mercies the remission of the temporal punishment due for their sins." The Church does this not just to aid Christians, "but also to spur them to works of devotion, penance, and charity" (CCC 1478). 

Also see, Primer on Indulgences.

Those in purgatory to not have to wait for people to obtain indulgences on their behalf to be released from purgatory. Their time in purgatory is over when the person is purified. Prayers and Indulgences for those in purgatory hastens the time in which the person will be released as indulgences take away some of the punishment due.

In simplest terms an indulgence is like this: You break my window on purpose. I forgive you for this sin, but the consequences of the sin (the broken window) still remains. You have an obligation to pay for the repair of the window. The replacement of the window will cost $500, but I am willing to reduce your obligation to $200 if you mow my lawn this coming summer.

In return for your good work (mowing) I have given you an indulgence of $300, that is, I have been lenient and charitable with you and reduced your obligation. This is a partial indulgence.

In essence, purgatory is a place where we pay for all the broken windows we did not get around to paying when we were alive in this world.

In a plenary indulgence the obligation is wiped out completely — to $0.00

As for those who do not understand, they may still have "broken windows". They will learn about what is happening at the time; God will inform them.

As for those who lack the capacity to understand, such as those with retardation, brain damage, mental illness, and the like, God's mercy is great. He will determine, according to His perfect justice, whether or not such people need to go to purgatory.

I hope this answers your questions.

God Bless,
Bro. Ignatius Mary