Does God forgives a sinner even if that sinner does not repent?

In one of the answers I read here some many said that we must forgive those who sinned against us even though they don't ask for forgiveness. They said that God forgave those who nailed him to the cross event though these people never repented. If that is so, why do we need to repent our sins then to God? All of us will go to heaven since we will all be forgiven.