John Wesley on Isaiah 42:21

Well pleased - Altho' God might justly destroy thee suddenly, yet he will patiently wait for thy repentance, that he may be gracious; and that not for thy sake, but for the glory of his own faithfulness, in fulfilling that covenant, which he made with thy pious progenitors. Magnify - He will maintain the honour of his law, and therefore is not forward to destroy you, who profess the true religion, lest his law should upon that occasion be exposed to contempt.