Joel's army is described in Joel 2:11, where the prophet predicts that an army, described as the LORDS army, will one day cover the land wreaking terror, pain, and destruction, but since Joel calls it the LORDS army, there is much confusion and debate about whether or not this army is a righteous host rather than demonic.
How can a demon (or demonized) host be called the LORDS army? The answer to that question is quite simple—the LORD calls the shots regardless of who is carrying out his will, and there are numerous examples in scripture of the LORD using Satan and/or his fallen angels in order to carry out his will or judgments. One clear example of this is found in 1 Kings 22:19-23 where the prophet Micaiah reveals God’s strategy [in using demonic spirits] for bringing down King Ahab for all his wickedness in leading Israel into Baal worship.
Micaiah is given a glimpse into Heaven where he sees the LORD surrounded by HIS armies, and asks who will persuade Ahab to go into a battle that would end in his death, and we read of a spirit volunteering to be a lying spirit in the mouths of Ahab’s prophets. No righteous angel could be a lying spirit, so the spirit that stepped up to the plate must have been a fallen angel.
It is interesting to note that the armies of the LORD that stood on his right side and on his left side included both holy angels and fallen angels (as evidenced by the lying spirit that came forward at the LORD’S challenge). Matthew 25:33, tells us that the sheep (righteous) are placed on the right hand of the King and the goats (unrighteous) are placed on his left hand. By that, it can be concluded that the armies on God’s right hand were holy angels and the armies on his left were fallen angels. That conclusion is legitimately debatable but nevertheless a valid consideration.
Like the lying spirit we read about in 1 Kings 22, the army described in Joel chapter two, is anything but a righteous army. But both the spirit and the army are agents of God in the evil tasks they are assigned to accomplish. The army Joel describes causes much pain and leaves widespread destruction in its wake.
The army Joel describes corresponds closely with the demon army described by John in the Revelation (Revelation 9). Very likely it is the same army. This demon army will bring great destruction during the Time of Jacob’s Trouble (The Great Tribulation).
The LORD’S army described in the book of Joel, is a demon (or demonized) army, used by the LORD in executing his judgment on a rebellious world during The Great Tribulation. It is called the LORD’S army, not because it is a righteous army, but because it is executing the will of God.