That is forgiving without limit. That is why Jesus used a big number, to show us that we must always forgive.
Ho many times God forgives us when we sin? Up to seven times? Up to seventy seven times? No he forgives us number of times without limit. That is why, he wants us to forgive without limit.
We may think think that for some of the worse situations in our life, when people sin against us, we can not forgive, because it hurts too much to forgive those who sin against us.
But forgiving is not forgetting. It is not about how we feel. It is about a choice made from us, based on our desire to forgive, because we have been commanded to by God.
God has commanded us to forgive others, because he has forgiven us. He wants us to be like him.
Forgiveness is a part of the image of God in us. The more we forgive, the more we look and act like God, and the brighter his image shines in us. It is about how much we want to be like him.