Behold, upon the mountains, the feet of him who brings good news, who publishes peace! Keep your feasts, O Judah; fulfill your vows, for never again shall the worthless pass through you; he is utterly cut off. The scatterer has come up against you. Man the ramparts; watch the road; dress for battle; collect all your strength. For the LORD is restoring the majesty of Jacob as the majesty of Israel, for plunderers have plundered them and ruined their branches.
There are three ways that this passage has generally been understood. Some have considered the plunderer to be Sennacherib, others Nebuchadnezzar. If this were referring to Sennacherib, the gist of the passage would be something like this: (a) Judah need not worry about Sennacherib, because while he is busy threatening you someone is preparing to attack him. Sennacherib will not attack you (God will restore your majesty…) because he is going to be attacked. (b) With the larger picture in view God is telling Judah that she may do all the guarding and preparing she wants, but this will all be of no avail because God will raise up someone else, after Nineveh, to teach rebellious Judah the same lesson Nineveh has been used of God to teach Israel.
(c) The third view is that this is addressed to Nineveh, in which can the plunderer would be Nebuchadnezzar. According to these interpreters, Nahum is proclaiming the ruin of Assyria like this, “Your destroyer is on the rise." The Assyrians would have viewed such a warning with disdain. 1:13 informs us that Assyria was at the height of her power when this prophecy was given. It was only after Assurbanipal retired from nearly a dozen military campaigns (one of which was against Thebes) did he return to Nineveh and gradually become indolent. It was then that the burgeoning unrest among his subjects the Babylonians and Medes break out into open rebellion. This is another factor that helps us date the book to the earlier part of the 50-year window between 663 BC and 613 BC. Nahum would be saying to Nineveh, “It won’t be how you’d expect it. The plunderer will not come secretly, but right in your face. You can guard the fortresses, watch the roads, and be as ready as you’d like, it will all be to no avail.” If this is the correct view, it will be confirming what has already been said that God had now determined to destroy Nineveh and the whole Assyrian Empire. Calvin takes issue with this view because if it were intended then something else should be stated to make it plain, such as -- that God now designed to destroy Nineveh and its monarchy, because it had humbled more than necessary his people, the kingdom of Judah, as well as the ten tribes.