John Gill Commentary Nahum 3:12

"All thy fortresses shall be [like] fig-trees with the first-ripe figs: if they be shaken, they fall into the mouth of the eater." — Nahum 3:12 (ASV)

All your 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 fall into the mouth of the
eater ;
as such ripe fruit is very desirable, and the mouth of a man is open and ready for them; so if he gives the tree but the least shake, they will fall into his mouth, or about him in great plenty: in like manner, as the fortresses of Nineveh, being of importance, were desirable by the Chaldeans and Medes, and for which they were gaping; so upon the least assault they would fall into their hands; see (Revelation 6:13) .