The invitation is followed by Jehovah's forgiveness through washing. Isaiah speaks of this in 1:18b. "Though your sins are like scarlet,/They will be as white as snow;/Though they are as red as crimson,/They will be like wool." Although His people were so sinful, God was willing to forgive them.
In 1:19 and 20 we have the issue of the people's obedience. If they were willing and listened, they would eat the good of the land. But if they refused and rebelled, they would be devoured by the sword.
In 1:26 and 27 we have the promise of restoration.
First, to save the people from their chaotic situation, God would restore the leaders. He promised to restore their judges as at the first and their counselors as at the beginning (v. 26a). This mercy from God would bring their situation back to its original condition.
There was also the promise to restore the city of Zion and its people. The city would be called the city of righteousness, the faithful city (v. 26b). Zion would be ransomed with justice, and her returning ones with righteousness (v. 27). They had become a chaos because they had given up justice and righteousness. But God's restoration would bring them back to the beginning.