Scholars think this letter of Jeremiah purporting to be sent to the exiles in Babylon is neither a letter nor written by Jeremiah, but dated sometime after the exile.
As in Sirach, the exiles deserve their punishment. Jeremiah (I'm using that name rather than keep saying "the author of this manuscript") warns them that when they get to Babylon, they will see many people worshipping many false gods. He counsels, "Don't be misled by these images made by people. They may be gold, but that gold has to be shined. They may have feet, but they can't walk. People may be offering sacrifices to them, but their priests use those gifts for themselves."
Still timely is the reminder that anything we can make for ourselves is finally an idol, a substitution for the true God.