But notice the contingency here spoken in the law, that they must call sin for what it is and it speaks of "paying for it", though not referring to the ultimate price of eternal condemnation but rather in the sense of the disciplines inherent in the curses mentioned in the law. But such discipline was meant to impart humility which leads to repentance. This is not unconditional forgiveness. But the forgiveness which is granted is absolute. This is the context in which the Isaiah passage must be considered.
"‘But if they will confess their sins and the sins of their fathers— their treachery against me and their hostility toward me, which made me hostile toward them so that I sent them into the land of their enemies— then when their uncircumcised hearts are humbled and they pay for their sin, I will remember my covenant with Jacob and my covenant with Isaac and my covenant with Abraham, and I will remember the land. For the land will be deserted by them and will enjoy its sabbaths while it lies desolate without them. They will pay for their sins because they rejected my laws and abhorred my decrees. Yet in spite of this, when they are in the land of their enemies, I will not reject them or abhor them so as to destroy them completely, breaking my covenant with them. I am the LORD their God. But for their sake I will remember the covenant with their ancestors whom I brought out of Egypt in the sight of the nations to be their God. I am the LORD.’"
It is interesting that on the one hand God considers sin so serious as to condemn people to the eternal fire of hell or if not at least into some serious discipline if repentance follows and yet when forgiveness is granted sin is viewed merely as a passing cloud, the morning mist which fades away. No man can redeem himself. Only God redeems. Only God forgives. Today's pop-psychology obsesses over a person forgiving themselves. That's irrelevant if God doesn't first forgive. So also Israel did not make God, but rather God made Israel. God created the nation of Israel. So also he made the Church of which Israel symbolizes.