There is a teaching that God has two attributes – Justice and Mercy. In His attribute of Justice, He may judge and punish. In His attribute of Mercy, he may forgive. What attribute God shows us depends on what we show our fellow people.
Many people who have been hurt, abused, mistreated, feel angry. They want Justice for their suffering. Their abusers must be punished for causing such pain. If a person wants this, he may get it. God may respond with His attribute of Justice, and punish the one who has done so much damage. However, if you want God to judge your oppressor, you also need to stand before Him and be judged.
If you want Justice, you need to make sure that you have behaved justly, that your actions have been righteous. If you have done evil, then you will also be judged, and possibly be punished.
Others may want God to treat them with Mercy. Maybe they know that they haven’t been particularly righteous; maybe they’ve been hurt so much that they just want God to be kind to them. If we want Mercy, we may get that, as well. But we need to ourselves be merciful. We can’t ask for Mercy, while harboring anger or ill will against others. Even if a person has abused us, if we want Mercy we need to show Mercy. That may involve forgiving someone who has caused us enormous suffering. To the extent that we want Mercy, we need to show Mercy.
So if you want Justice, you must ensure that you have behaved righteously. Otherwise, you are likely to be punished, even as you want your oppressors to be punished. If you want Mercy, you must ensure that you show Mercy to others; you must forgive.
There is the prayer that goes, “..forgive us our trespasses, as we forgive those who trespass against us.” To the extent that you show mercy to others, God will show Mercy to you. If you want to be forgiven, you need to forgive.