Commentaries:
Jamieson, Fausset, and Brown
The nations hostile to Israel are summoned by Jehovah to "come up" (this phrase is used because Jerusalem was on a hill) against Jerusalem, not that they may destroy it, but to be destroyed by the Lord (Eze. 38:7-23; Zechariah 12:2-9; Zechariah 14:2-3).
Prepare war—literally, sanctify war: because the heathen always began war with religious ceremonies. The very phrase used of Babylon's preparations against Jerusalem (Jeremiah 6:4) is now used of the final foes of Jerusalem. As Babylon was then desired by God to advance against her for her destruction, so now all her foes, of whom Babylon was the type, are desired to advance against her for their own destruction.
Other Jamieson, Fausset, and Brown entries containing Joel 3:9:
Isaiah 13:3
Joel 3:11
Revelation 19:20
DISCLAIMER: Church of the Great God (CGG) provides these resources to aid the individual in studying the Bible. However, it is up to the individual to "prove all things, and hold fast to that which is good" (I Thessalonians 5:21). The content of these resources does not necessarily reflect the views of CGG. They are provided for information purposes only.