Hi, Meredith —
Sure, no problem.
Purgatory is what is referred to in 1 Corinthians, Chapter 3:
10 According to the commission of God given to me, like a skilled master builder I laid a foundation, and another man is building upon it. Let each man take care how he builds upon it. 11 For no other foundation can any one lay than that which is laid, which is Jesus Christ. 12 Now if any one builds on the foundation with gold, silver, precious stones, wood, hay, straw — 13 each man's work will become manifest; for the Day will disclose it, because it will be revealed with fire, and the fire will test what sort of work each one has done. 14 If the work which any man has built on the foundation survives, he will receive a reward. 15 If any man's work is burned up, he will suffer loss, though he himself will be saved, but only as through fire.
(The Holy Bible. (2006). (Revised Standard Version; Second Catholic Edition, 1 Corinthians 3:10-15). San Francisco: Ignatius Press.)
Basically, all of our works will be tested to see which ones are valuable and which ones are dross. The term Purgatory means cleansing and it's in the state of Purgatory that all that is non-precious in our lives is cleansed from us. Note that in this verse, it speaks of someone suffering loss but being saved, but only as through fire. So it isn't Hell, because those in the state of Purgatory are saved; but it isn't Heaven because, for those in this state, suffering is involved.
Purgatory is the anteroom to Heaven; everyone who encounters Purgatory is saved and will eventually enter Heaven and so will be resurrected on the Last Day. We believe that we can help those in Purgatory by praying for them. This is testified to by an ancient Jewish document known as 2 Maccabees in 2 Maccabees 12:43-45. (We consider this Scripture, but it's valuable even as a historical document.) Here there was a battle and certain men fell dead in the battle. It was discovered that they were wearing amulets sacred to a foreign god, proving that they had sinned. So they took up a collection to make a sin offering for them for their souls:
43 He also took up a collection, man by man, to the amount of two thousand drachmas of silver, and sent it to Jerusalem to provide for a sin offering. In doing this he acted very well and honorably, taking account of the resurrection. 44 For if he were not expecting that those who had fallen would rise again, it would have been superfluous and foolish to pray for the dead. 45 But if he was looking to the splendid reward that is laid up for those who fall asleep in godliness, it was a holy and pious thought. Therefore he made atonement for the dead, that they might be delivered from their sin. [a]
[a] 12:45 Vulgate has (verses 45-46): '45 And because he considered that they who had fallen asleep with godliness bad great grace laid up for them. 46 It is therefore a holy and wholesome thought to pray for the dead, that they may be loosed from sins.'
Catholicism only requires the assent of two propositions with respect to Purgatory:
- That it exists, and
- That those who are in it can be helped by our prayers.
As for Mary — well that is an extremely large topic. I recommend the book, Behold Your Mother by Tim Staples. The main point of Mary is that her role is to lead us to Jesus.
"Do whatever He tells you." (John 2:5)
She helps us to live out the Gospel of Christ, by both her example and her heavenly intercession. One thing to keep in mind about Mary is that she is the exemplar of the Church, that is to say, she sums up, represents, or recapitulates everything that is true about the Church (Matthew 12:49). She is immaculate (spotless). She is Mediatrix. (i.e. she intercedes for us from Heaven.) She has received the same resurrection we will receive in her Assumption into Heaven. She fill[s] up in [her] own flesh what is still lacking in the sufferings of Christ (Colossians 1:24). She is the Queen of Heaven (Revelation 5:10). She crushes the head of the serpent (Romans 16). In a sense when we praise or honor Mary, we are experiencing a taste of our own destinies if we persevere to the end. An interesting passage to meditate on is Psalm 45. This describes the glory of Mary, the Queen (also see Revelation 12:1) — first it starts of describing the Messiah:
6 Your divine throne endures for ever and ever. Your royal scepter is a scepter of equity;
7 you love righteousness and hate wickedness. Therefore God, your God, has anointed you
with the oil of gladness above your fellows;
8 your robes are all fragrant with myrrh and aloes and cassia.
From ivory palaces stringed instruments make you glad;
9 daughters of kings are among your ladies of honor; at your right hand stands the queen in gold of Ophir.
Then it addresses the Queen:
10 Hear, O daughter, consider, and incline your ear;
forget your people and your father's house;
11 and the king will desire your beauty.
Since he is your Lord, bow to him;
12 the people of Tyre will court your favor with gifts,
the richest of the people with all kinds of wealth.
13 The daughter of the king is decked in her
chamber with gold-woven robes;
14 in many-colored robes she is led to the king,
with her virgin companions, her escort, in her train.
15 With joy and gladness they are led along as they enter the palace of the king.
16 Instead of your fathers shall be your sons;
you will make them princes in all the earth.
17 I will cause your name to be celebrated in all generations;
therefore the peoples will praise you for ever and ever.
(Revised Standard Version; Second Catholic Edition, Psalm 45:6–17).
Here we have the queen of the Messiah bedecked in gold.
In the Near Eastern world, the mother of the king was the queen, not the bride of the king, because these peoples were polygamous. Of course the Queen here can also represent the Church, but that's part of the point; the symbolism of the Church is united with the symbolism of Mary.
Here the queen is plied with gifts for her favor, that is, for her Heavenly intercession. She has spiritual sons (see Revelation 12:17) whom she makes princes (again, in an intercessory role). The I will cause your name to be celebrated in all generations; therefore the peoples will praise you for ever and ever (Psalm 45:17) echoes All generations will call me blessed (Luke 1:48).
As one Orthodox hymn has it, she is higher than the cherubim, more glorious beyond compare than the seraphim, that is, the most exalted creature ever created. And that, again, represents the destiny of the Church as a whole.
There is much more to be said about Mary. If you are up for an exhaustive biblical treatment of the topic, buy or borrow the Tim Staples book I referred to above.
If you want to delve more gingerly into it, check out these articles on the topic: