Enemies of Israel often march into battle convinced they are acting on their own free will and independent power. They believe they are the masters of their destiny, completely unaware that they are merely instruments in a much larger Divine plan. Because history has not yet witnessed an event that perfectly matches this scenario, this prophecy points toward the distant future, specifically to the End of Days and the ultimate war of Gog and Magog [אבן עזרא, רש״י]. In that time, the nations of the world will advance upon Jerusalem with the clear intention to plunder its wealth and leave it in ruins [רד״ק].
However, they are completely blind to God's true design. In reality, it is God Himself who stirs their spirits and plants the desire in their hearts to gather at Zion, drawing them into a trap for their own downfall [רד״ק, מצודת דוד]. There is a profound depth to their ignorance. They fail to recognize both the immediate steps God takes to orchestrate events and His ultimate, final goal. Even if they could somehow perceive the methods God uses to bring them together, they lack the deep understanding required to comprehend the true reason they have been assembled [מלבי״ם].
To illustrate this Divine trap, a vivid image from the world of farming is used. The nations are compared to bundles of grain brought to a threshing floor. A farmer does not gather sheaves of grain to protect them, but rather to beat and thresh them. In the exact same way, God gathers the nations around Jerusalem not for their victory, but for their destruction [רש״י, מצודת דוד].
This dramatic gathering serves a twofold purpose. On a national level, during the time of the ingathering of the exiles, the very place where these nations—particularly the Christian kingdoms—committed their wicked acts will become the site of their final judgment. There, Israel will be the one to break and thresh its enemies [אברבנאל, רד״ק]. On a spiritual level, the war will act as an actual threshing process. It will violently separate the wicked, who will be blown away like useless chaff in the wind. All that will remain is the pure, clean grain, representing the righteous converts and those who finally recognize the true faith [מלבי״ם].