Honest question: If I am in a state of grace (if I am saved) then what does an indulgence do for me?
Thanks for an honest question. Really. On this forum it's kinda-like refreshing. Let's see if I can make sense of this without taking up too much bandwidth.
The Bible says there are three parts to repentance: (1) contrition, (2) confession, and (3) bringing forth fruits worthy of repentance. It's the third part --- not #1 and #2 --- that is related to indulgences, which the Catholic Church also calls "satisfaction". Some Bible translations use the phrases do penance or the word penance where other use repent and repentance but the meaning is the same: it means to "make satisfaction" for sin.
This was addressed by St. Paul to the Colossians --- believing Christians who lived in Colossae ---in the 50s while Paul was in prison. Notice that this is very early, and that its audience was forgiven sinners (believers) and yet that Paul says there will be repayment for "anyone" and "no favoritism."
You are forgiven (your eternal relationship to Almighty God is intact). You are fully in His good will. But wrongs still have to be paid for.
Wait--- what? Didn't Jesus pay it all by dying for us?
Yes, because He won for us what we could never-in-a-million-years have won for ourselves: life eternal! But it's to these saved people that Paul says "wrongs have to be paid for." He is NOT talking about eternal consequences (that's been paid in full). He's talking about temporal consequences.
Why? Because
He confesses his sin to his Dad. And he gets his answer: "Yes." But although the kid is truly sorry he did it and Dad forgives him (he hasn't disowned you, his wrath is turned away, in fact, you are back in his strong hug!) the car is still wrecked and you still have a broken leg.
You have repented, you have confessed, (thus you are forgiven) --- you feel great peace over that --- but that third thing, "bringing forth fruits worthy of repentance," still has to be done.
In this case, it probably means some painful rehab for the leg, and some payback to get the car repaired.
That's what a "penance" is for and that's what an "indulgence" is for.
This is about rehabbing your soul and restoring the balance of justice.
I am just trying to make that those two preliminary points, for now.
This is quite incomplete. It's Part 1. I'm sure you have more questions. If you want to ask them, I could go on to Part 2.