Let’s extend the analogy.
Imagine that the debtor who owed $100,000.00 had a wealthy friend - an infinitely wealthy friend - and not only that, his friend is extremely generous. But, he doesn’t want to be taken advantage of by the unscrupulous, so he wants to make sure that when he bails someone out of their troubles, that they will be appropriately grateful. So, he asks for some sign or token to signify the sincerity of the person’s request - maybe he hires the person, or the person’s children, to do some kind of simple job or jobs in his office, or at his home, or something like that. Nothing arduous, but just something that keeps the lines of communication open, and allows him to see how the person is doing.
Then, this wealthy friend pays the debt, but not only the debt of that man, but
also the debts of everyone who was affected by the non-payment of the debt (since, if you have ever had someone not pay you back something they owed you, you know that you yourself go into debt, as well, because of not having the money at the time that you were expecting to have it). So, the wealthy friend finds all these people, compensates them for the interest they had to pay and the trouble that they went through - for example, if one of the children got sick and missed school because of the stress that the family was undergoing when they didn’t get their money paid back, the wealthy friend sends a tutor over to help the child get caught up with his school work, and gives the child something that will help him to restore his relationship with his friends at school.
The Treasury of Merits is nothing other that Jesus Christ on the Cross - and this is an infinite treasury of merit. Jesus is our infinitely wealthy friend.
We see a kind of model of Purgatory when we look at Jesus’ parable of the slave who had a debt to his master that he could not pay - a debt of such an astronomical amount that there was no way he was ever going to be able to pay it back.
He goes to his master, who threatens to put him in prison and sell his family, along with all of their possessions.
He weeps and pleads, and the master relents and releases him from the debt.
Now, if he is sincere, then he gets to keep this Indulgence. So, when he encounters the slave who owes him some piddling amount (we’ll say that this second slave is a soul in Purgatory) - if he is sincerely repentant, he remembers the generosity of his master and seeks to imitate it, so he releases his fellow slave from the small debt, and thus,
both of them are free.
However, in actuality, his tears were crocodile tears; he was
not sincerely repentant, so as soon as he was free, he sought to make good on his own debts, so he went after his fellow slave, and threw him in prison for the small piddling amount that this other slave owed him. His master heard about this, became enraged, and followed through on his original threat - he lost the Indulgence, because he was not
truly repentant for his sins.