"Undoubtedly the Hebrew people considered the Assyrians to be the most “godless” and “profane” people they knew. Yet, Isaiah has the audacity to say that the Assyrians are God’s tool to punish them and that they are the godless and profane ones! How could this be? First, it is plain that the prophet considers all peoples to be instruments of the Sovereign. Even the vilest of persons is serving God’s purposes, if only to illustrate the ultimate results of evil. This is not to say that God manipulates people in a cynical way. It is to say that God is present in and through the processes of history, bringing out of them that which will most effectively serve goodness and truth. But second, there is a relativity of accountability. Relatively speaking, Israel is more profane and godless than Assyria because she has had more light to reject. If her moral state is still higher than Assyria’s, it is also true that she has fallen the farther distance. So Jesus’ words, “To whom much is given, much is required” (Luke 12:48), apply to Israel and Assyria; they also apply to the modern West."
(Oswalt, John N. The Book of Isaiah, Chapters 1–39. The New International Commentary on the Old Testament. Grand Rapids, MI: Wm. B. Eerdmans Publishing Co., 1986, 263.)