Adam Clarke on Jeremiah 10:2

Learn not the way of the heathen - These words are more particularly addressed to the ten tribes scattered among the heathen by the Assyrians, who carried them away captive; they may also regard those in the land of Israel who still had the customs of the former heathen settlers before their eyes.

Be not dismayed at the signs of heaven; for the heathen are dismayed - The Chaldeans and Egyptians were notoriously addicated to astrology; and the Israelites here are cautioned against it. The signs of the heavens may mean either the sun, moon, planets, and particular stars or constellations; or the figures or characters by which they represented these heavenly bodies.