The major theme of Nahum is the judgment of God. God is a just God who will judge the guilty. His wrath will not be resisted and those who think they will not fall before it deceive themselves.
Linked to this overriding theme are the themes of sin and restoration for God’s people. The judgment is occasioned by the sin of Nineveh, most notably its vicious treatment of other nations. God’s judgment of Assyria, which Isaiah identified as a rod of God’s chastening, marked the hope that God would restore his people (1:2, 12-3, 15; 2:2; 3:19).
O. Palmer Robertson observes “the absence of virtually a trace of messianism” in this book. But while the hope of the messianic Davidic king is not a theme of this book, Jesus is Yhwh, and he will come in the last day to judge the nations as Nahum foretold.
 Robertson, NICOT, 17.