CS Lewis in his classic Mere Christianity wrote:

‘The one most people have heard is the one I mentioned before–the one about our being let off because Christ had volunteered to bear a punishment instead of us. Now on the face of it that is an absurd theory. If God was prepared to let us off, why on earth did He not do so? And what possible point could there be in punishing an innocent person? None at all that I can see, if you are thinking of punishment in the police-court sense. On the other hand, if you think of a debt, there is plenty of point in a person who has some assets paying it on behalf of someone who has not.’ (emphasis added)

Except that Jesus taught that even a debt could be forgiven by God.

In Matthew 18 we read Jesus’ teaching:

The Kingdom of Heaven can be compared to a king who decided to bring his accounts up to date with servants who had borrowed money from him. In the process, one of his debtors was brought in who owed him millions of pounds. He couldn’t pay, so his master ordered that he be sold—along with his wife, his children, and everything he owned—to pay the debt.

“But the man fell down before his master and begged him, ‘Please, be patient with me, and I will pay it all.’ Then his master was filled with pity for him, and he released him and forgave his debt.

“But when the man left the king, he went to a fellow servant who owed him a few thousand pounds. He grabbed him by the throat and demanded instant payment.

“His fellow servant fell down before him and begged for a little more time. ‘Be patient with me, and I will pay it,’ he pleaded. But his creditor wouldn’t wait. He had the man arrested and put in prison until the debt could be paid in full.

“When some of the other servants saw this, they were very upset. They went to the king and told him everything that had happened. Then the king called in the man he had forgiven and said, ‘You evil servant! I forgave you that tremendous debt because you pleaded with me. Shouldn’t you have mercy on your fellow servant, just as I had mercy on you?’ Then the angry king sent the man to prison to be tortured until he had paid his entire debt.

“That’s what my heavenly Father will do to you if you refuse to forgive your brothers and sisters from your heart.”

So God freely forgives our sins and expects us to forgive our neighbour too. The Lord’s Prayer, of course, has the same commandment.

Jesus’ teaching finds an echo in the Quran where God speaks words of encouragement:

“O my Servants who have transgressed against their souls! Despair not of the Mercy of Allah: for Allah forgives all sins: for He is Oft-Forgiving, Most Merciful.”

The Prophet Muhammad (pbuh) said:

The Most Merciful shows mercy to those who have mercy on others. Show mercy to those on the earth and the One above the heaven will show mercy to you.”