Charles Ellicott Commentary Jeremiah 4:5

"Declare ye in Judah, and publish in Jerusalem; and say, Blow ye the trumpet in the land: cry aloud and say, Assemble yourselves, and let us go into the fortified cities." — Jeremiah 4:5 (ASV)

Declare. — that is, proclaim as a herald proclaims. The cry is that of an alarm of war. The prophet sees, as it were, the invading army, and calls the people to leave their villages and take refuge in the fortified cities.