God asks the children of Israel how their mother (apparently, Israel in the abstract) could have received a bill of divorce from him, from God.
He answers his own question: they were separated from God because of their sins.
No one answered God's call to redemption (which, he reminds you, he totally could've pulled off had anyone been willing), so he dried up the seas and killed fish and made the sky black as though it were covered in sackcloth.
Now, somebody's (Isaiah? A future Messiah? A past historical figure?) voice jumps in, discussing how he was appointed God's servant, and had his ear opened to the Lord's word.
He had to put up with a lot of abuse—people spitting on him and pulling his beard—but he didn't give up.
Isaiah says that God is his ally and challenges any of his enemies to confront him.
Those enemies are just going to get worn out like clothes eaten by moths. (Classic smack talk.) He challenges everyone to fear the Lord and follow him, but ultimately concludes that they're all burning themselves with their own fires and will be forced to fall into torment.