The LORD also shall roar out of Zion, and utter his voice from Jerusalem; and the heavens and the earth shall shake: but the LORD will be the hope of his people, and the strength of the children of Israel.
The Prophet explains here more clearly his object, or the end for which he had hitherto spoken of God’s judgment; for what we have heard served only to spread terror: but now the Prophet shows that his purpose was to console the faithful, and to give some relief to their troubles and sorrows. This is the reason why he introduces God as roaring from Zion and crying from Jerusalem.
This call to the nations to prepare war is spoken ironically: let all forces confederate against God if they dare. They are summoned to the battle of that great day when God shall judge the earth, gathering all nations to their ruin.
AI summary
Commenting on Joel 3:9-17
The Lord also shall roar out of Zion, and utter his voice from Jerusalem,.... Christ, the Lamb, shall now appear as the Lion of the tribe of Judah, and utter his voice in his providence and judgments on the behalf of his church and people, signified by Zion and Jerusalem; and therefore said to roar, and utter his voice from thence; he will be heard...