John Oswalt writes this in his commentary.
"Of all the books in the Old Testament, Isaiah is perhaps the richest. Its literary grandeur is unequaled. Its scope is unparalleled. The breadth of its view of God is unmatched. In so many ways it is a book of superlatives. Thus it is no wonder that Isaiah is the most quoted prophet in the New Testament, and along with Psalms and Deuteronomy, one of the most frequently cited of all Old Testament books. Study of it is an opportunity for unending inspiration and challenge."