NOTES for Isa 43:24-25
So, the Lord says that His people have forgotten everything He did for them, forgotten all His wonders. And once again He performs wonders for His people. Why? After all, the people did not cry out to Him, did not offer sacrifices, did not ask for help... All the people did was hinder God from acting in their lives: burdening Him with sins and weighing Him down with iniquities, as the prophet Isaiah says. Why, then, does the Lord blot out all iniquities and agree not to remember sins?
And the answer He gives here is universal. He says: "For My own sake." He is ready to forget sins not because the people have corrected themselves or politely asked. He forgives because He is good and merciful, because He loves.