Just like we have an obligation to defy the unjust and harmful things that other people do, we have an obligation to resist, oppose, rebuke, and undo the unjust and harmful things that we ourselves do.
Basically, we have to try to reverse the harm that we've done -- that is, try to restore things as best we can to the way they were before we did whatever harm we did -- and to redeem ourselves -- that is, fix whatever flaw in our character led us to do that unjust or harmful thing. You can't receive forgiveness without any effort: you have to earn it through some process of atonement.
How precisely this is to be done in any given situation is difficult to say. There are lots of different degrees and ways in which we mistreat one another. Some of them are minor (e.g., I'm late for lunch with a friend), some of them are severe (e.g., I kill someone), and some of them are intangible (e.g., I cheat on my spouse, or lie to someone who has put their trust in me).
There is probably no simple formula that can cover all these diverse cases, but it looks like the following things play important roles:
Admission of Guilt
It's important that you admit that you did something wrong, and do so to the person or people you harmed (rather than just confessing privately to yourself that you screwed up).
Related to the above, there should be an expression of sincere remorse or regret for the harm you've caused, something that demonstrates a true understanding of how you've mistreated others, and expresses sympathy with the pain that you have caused.
We have to be careful with apologies, however. There's a selfish tendency to think that all you have to do to earn forgiveness is apologize (which is not often the case), and to give apologies motivated by regret for having gotten caught (rather than motivated by remorse for having caused harm to someone).
Restitution and Making Amends
We have to do our best to undo the harm we've caused, or give compensation for it. Sometimes this is easy: if I break your $100 table, I should at least fix the table or give you $100. But, if I kill someone, I can't bring them back, and I can offer very little to replace them.
Similarly, if I cheat on my spouse, the intangible harm I've caused is very difficult to undo or compensate for. I don't mean to say that acts such as murder or adultery are unforgivable, but they are certainly not easy things to undo. If it is possible to earn forgiveness for them, the process involved is likely to be arduous and slow.
Redemption and Changing Our Character
We have to rid ourselves of the flaws in our character that led or allowed us to do the unjust thing that we did, so that we don't do it again. Perhaps we were greedy, or careless, or ignorant of how to respect others. Whatever, we should work to replace our vices with virtues.
This can take a lot of time. For instance, if I've betrayed somebody's trust in me -- by lying or not keeping a promise to them -- it may take a while for me to prove that I'm worthy of being trusted again.
With respect to forgiveness, there are also obligations for those who have been harmed.
For instance, if someone has done everything that can reasonably be done to earn forgiveness, then it's wrong for us to withhold it. It is tempting, as a victim, to torture the people who have harmed us by refusing to forgive them no matter what they do. But this is itself an unjust, selfish, and harmful thing to do.
Likewise, when you've forgiven someone for something, you shouldn't bring it up in order to criticize them. Any mistake they've been forgiven for is a mistake that has been addressed and put in the past; it is unfair to bring it once again into the present.
It's also important for a victim to not hold a grudge against the person who has harmed them, whether or not that person has earned forgiveness. The worst thing a victim can do to themselves is to fester on and on about how they've been mistreated, refusing to make any success or progress in their lives until the person who has treated them unfairly apologizes and makes amends. If anything, it's just poor planning, because it's clear that many people just aren't going to live up to their obligation to reverse or repair the harm they've done.
Even with these rough guidelines in mind, there's an awful lot left unclear regarding forgiveness:
- Is it possible to earn forgiveness for irreversible harms (such as murder, or adultery)? Can forgiveness only be given in such cases, not earned?
- What role, if any, does punishment play with respect to forgiveness? Is it necessary for me to be punished in order to earn forgiveness? What purpose is punishment supposed to serve?
- If I forgive someone, must I also reconcile with them (that is, retain the same relationship I had with them previously)? I forgive my spouse for cheating on me: does that mean I must remain married to them?
None of these are easy issues. But they are enormously important ones, because it's impossible to go through life without mistreating others in some way or another, intentionally or unintentionally. And it's just not acceptable to say "well, shucks, we're all human, we all make mistakes" as if that settles the matter.
Yes, we're clearly capable of making mistakes, but we're also clearly capable of taking responsibility for and repairing those mistakes in significant ways. And that's what forgiveness is all about: undoing the mistakes we inevitably make in how we treat one another.