A massive historical event is about to unfold, one so public and undeniable that no messengers will be needed to carry the news or verify its truth. The message will echo across the globe, reaching every corner of the earth. The call goes out to all of humanity, leaving no one behind. It speaks to both permanent residents and temporary travelers, reaching those in populated regions as well as those in barren, desolate lands [מלבי"ם]. Every person, regardless of where or how they live, will be a witness.
To illustrate how widely known this event will be, vivid imagery is used of a tall flag raised high on the mountains to be seen from afar [מצודת ציון, ביאור שטיינזלץ], alongside the loud blast of a horn. The primary approach among commentators is that these are not physical objects meant to be used literally. Rather, they serve as a poetic metaphor showing that the unfolding events will be unmistakably clear to the eyes and ears of all people [רד"ק, שד"ל, חומת אנך].
What exactly is this world-altering event? The primary approach among commentators views this as a message of salvation, specifically the gathering of the exiles and the return of the people of Israel to their homeland. Just as a leader might raise a flag and sound a horn to assemble a nation, God will gather Israel, and the entire world will watch and listen firsthand [רש"י, מצודת דוד, רד"ק].
Another perspective suggests a different kind of divine intervention, pointing to the miraculous downfall of Sennacherib, the King of Assyria. God's strike against the Assyrian army will be so powerful and decisive that the news will spread globally, as obvious as a giant banner waving over the whole earth [אבן עזרא].
In sharp contrast, a third approach reads the impending event not as a moment of salvation, but as a severe threat of war. According to this view, the speakers are actually the messengers of the Assyrian king, warning the world that no one can escape their empire. They declare that very soon, all nations will see the flags of war raised on the mountains and hear the terrifying sound of the battle cry closing in on them [מלבי"ם].