The verse "For they can neither curse nor bless kings:" from Jeremiah's Letter (also known as the Letter of Jeremiah) 6:66 (or verse 6:60 in some numbering systems) is part of a polemic against idolatry. The Letter of Jeremiah is an appendix to the Book of Baruch in the Septuagint (the Greek translation of the Hebrew Bible) and in the Vulgate (the Latin translation of the Bible), and it is considered deuterocanonical. It purports to be a letter written by the prophet Jeremiah to the Jewish exiles in Babylon, warning them about the dangers of idolatry.

In context, the verse emphasizes the impotence and uselessness of idols. Here's a breakdown of the meaning:

"They": Refers to the idols mentioned in the letter.
"can neither curse nor bless kings": This means the idols have no real power or influence over even earthly rulers, let alone the destinies of individuals or nations. They can't bring misfortune (curse) or prosperity (bless).

The purpose of the verse is to highlight:

The lack of agency in idols: They are inanimate objects, incapable of performing any real action, whether good or evil.
The foolishness of worshipping idols: Why would anyone fear or revere something that cannot affect their lives in any way?
A contrast with the true God: This statement implicitly contrasts the powerless idols with the one true God, who does have the power to bless and curse, to influence events, and to hold kings accountable.

In essence, the verse is a sarcastic jab at idolatry, ridiculing the notion that these statues have any divine qualities or power.