Jamieson, Fausset and Brown on Jeremiah 27:3

3. And send them to the king of Edom, &c.--Appropriate symbol, as these ambassadors had come to Jerusalem to consult as to shaking off the yoke of Nebuchadnezzar. According to Pherecydes in Clement of Alexandria [Miscellanies, 567], Idanthura, king of the Scythians, intimated to Darius, who had crossed the Danube, that he would lead an army against him, by sending him, instead of a letter, a mouse, a frog, a bird, an arrow, and a plough. The task assigned to Jeremiah required great faith, as it was sure to provoke alike his own countrymen and the foreign ambassadors and their kings, by a seeming insult, at the very time that all were full of confident hopes grounded on the confederacy.