Isaiah as a Summary of Biblical Theology

There is no other book in either Testament which comprehends the whole of biblical theology so completely as does Isaiah.

Here the terrifying holiness of God is depicted as clearly as it is anywhere in the OT, but also the unchanging grace of God is depicted as clearly as it is anywhere in the NT. Thus in many ways the book of Isaiah offers a summary of biblical theology.

—John Oswalt, "Isaiah," New Dictionary of Biblical Theology, 217.