Before diving in, set aside everything you think you know about indulgences. Because the odds are strong you've been given the wrong idea.
An indulgence is a gift of mercy, made possible by Christ himself, but given to the faithful through the ministry of the Church, by virtue of the "power of the keys" conferred by Christ himself, first on Saint Peter in a particular way (Matthew 16), but on the Apostles as a college, and thus the Church through her apostolic leaders (Matthew 18).
OK, did you read that? Did you notice it's (a) a gift...(b) of Christ himself?
But wait, you say -- isn't there something about our own works? And isn't it some sort of way to get off the hook for sins?
An indulgence is granted, by the Church, in conjunction with various acts of faith and charity. The rationale for attaching indulgences to various works isn't hard to see, once you see what they are. Some are spiritual works of mercy, such as visiting a cemetery; some are actions that are aimed at increasing ones own faith, such as a pilgrimage, or visits to particular holy places.
So what does an indulgence do?
An indulgence is the remittance -- the wiping away -- not of sins (which is available through sorrow and repentance, ordinarily through the sacrament of confession), but of the eternal consequences of sin. In other words, an indulgence is a relief for those undergoing purgation -- i.e., Purgatory. Some indulgences are "partial," others are "plenary" or full. The one I obtained today is the latter.
So what do you do with an indulgence? Well, you can do two things. You can offer it to God for your own soul; or you can offer it to God for the souls of those in purgatory -- which is what I always do.
You might well wonder, how does this work? Did someone in Purgatory get a visit from an angel, get escorted out, "courtesy of Father Martin Fox"?
I dunno. But doesn't it make sense that the sharing all the Body of Christ have in the life of Christ should not be overpowered by death? Just because we have no real sense of what is going on in heaven or heaven's front porch (purgatory), doesn't mean they are in the same boat.
It makes perfect sense to me that the souls in purgatory are well aware of both heaven and us. And if there is any suffering in purgatory -- and it makes sense that there would be, since there's suffering here -- isn't it a very happy thought that in some way, they receive some sort of relief or encouragement, and know it's from our prayers and offerings?
And here's another angle on this. You need to furrow your brow and really fire up your synapses to get this idea. Ready?
Where is it written that when we offer prayers and sacrifices for "the dead," that God is limited to applying them...only for people when they're dead?
I prayed for my parents during Mass today. Because they're dead as of AD 2014, does that mean that God is somehow handcuffed, and can only respond to that prayer in terms of what he might do for my parents in the afterlife? Who boxes God in in this way? Not I. Who then?
Consider, then, that when we pray for anyone, in particular for the dead, God is well able to apply those prayers at any point in that person's life. Including in what is -- to us -- the past!
Now, some people might look at this, and might not care for it. It doesn't help that many people, even priests, don't really understand what indulgences are. But why not step back and look at the larger picture here -- look at what the Church is actually doing.
Holy Mother Church is trying to foster both growing in faith, and in charity -- and the conditions of the indulgence, when you think about it, boil down to one word: conversion. If you want to get this grace, convert.
Of course, the Church could just say that. And she does. Over and over.
With indulgences, the Church is saying it a different way. In a way that helps get many people onto the path of conversion.