All your fortresses are like fig trees with first-ripe figs— if shaken they fall into the mouth of the eater.
The Prophet here declares that the strongholds of the Assyrians would avail them nothing; whether they trusted in the number of their men, or in their walls, or in other defenses, they would be disappointed; for all things, he says, will of themselves fall, even without being much assailed.
Nineveh has been told that God is against her, and then none can be for her, to stand her in any stead; yet she sets God himself at defiance, and his power and justice, and says, I shall have peace. Threatened folks live long; therefore here the prophet largely shows how vain her confidences would prove and insufficient to ward off the judgment of God.
Commenting on Nahum 3:8-19
All thy strong holds shall be like fig trees with the first ripe figs,.... Upon them, or like them: "and the first ripe figs"; which are easily shook and gathered; and so easily should the fortresses and towers of Nineveh, in which they trusted for safety, be taken by the enemy, not only one, but all of them: if they be shaken, they shall even...