Isaiah 18:3

3. See ye, when, etc. The picture takes in the prophet as saying to all the people in those far lands, “Be ready when ye shall see the signal raised on the mountains; note it, when the trumpet shall sound; listen, and be on the alert.” The prophet’s alarm is in the interest of Judah, or, which is the same thing, of Jehovah’s cause. The passage-way of the armies of the rival empires lay through Judah, now a dependent of Egypt, on account of which dependence Judah is to suffer if Assyria prevails. The implied prediction is, that God is about to deliver the world from the all-conquering might of Assyria.