For ... from Dan - The connection is: There is danger in delay; for the voice of a messenger announces the approach of the Chaldean enemy from Dan, the northern frontier of Palestine (Jer 8:16; compare Jer 4:6; Jer 1:14).
Mount Ephraim - which borders closely on Judah; so that the foe is coming nearer and nearer. Dan and Beth-el in Ephraim were the two places where Jeroboam set up the idolatrous calves (1Ki 12:29); just retribution.