This verse, from the apocryphal Letter of Jeremy (also known as the Letter of Jeremiah), is a satirical condemnation of idolatry. It's a rhetorical question designed to highlight the absurdity of worshipping idols. Here's a breakdown of its meaning:

"How then can’t men understand...": This sets up the argument, implying that the point is so obvious that it's incomprehensible how anyone could miss it.

"...that they be no gods...": The core assertion: these idols or statues aren't real gods.

"...which can neither save themselves from war, nor from plague?": This is the key reason why the idols aren't gods. Real gods would have the power to protect themselves and their worshippers from calamities like war and plague. Since these idols are powerless even to defend themselves, they clearly lack divine power.

In simpler terms, the verse is saying: "How can people be so foolish as to think these idols are gods? They can't even save themselves from being destroyed in war or stop a disease from spreading! Real gods would be able to do these things."

The overall message is a critique of idolatry by pointing out the powerlessness and uselessness of idols, especially during times of crisis. It's a polemic against worshipping objects that have no real power. The Letter of Jeremy uses such arguments to discourage Jews from being influenced by the idolatrous practices of Babylonians.