Justice is really very simple. Refer to the "golden rule"

If you made a mistake, how would you want someone to treat you? If someone makes a mistake you should be just as forgiving as you would want them to be.

And guess what? That is the teaching of Jesus. Forgive us our debts AS we forgiver our debtors.

The bible is full of examples of this karma like reap what you sow eye for an eye or forgiveness for forgiveness concept.