In this passage we see the Second Coming of Christ. In reading it you might notice that Jesus and His followers will come from heaven to the earth on horses, they are called the armies of heaven. Jesus comes to judge with “justice” and to make “war.” I think this is the final war that Joel speaks of here in chapter 3. In Revelation 19:17-21 we see the gathering of great armies where there are kings, generals and mighty men plus people of all kinds, free and slave, great and small, all waging war against God’s precious Son. Verses 19 through 21 speaks of armies and the beast trying to make war against the “Rider on the horse” and His armies. But the old beast who was captured and the false prophet were thrown alive in the fiery lake of burning sulfur. Verse 21 says, “The rest were killed with the sword that came out of the mouth of the Rider on the horse, and all the birds gorged themselves on their flesh.”
We have just spoken of the “war” that Joel speaks of in the Valley of Decision.
I don’t really know this to be exactly the way it will be. Does anyone? But because there will be what I and many others believe, as described in Chapter 20 in Revelation, a 1,000 years reign of the Lord Jesus Christ, where He makes all things right and reigns for the millennium in peace and harmony, in the world rejuvenated from the destruction mankind has caused. We see some of that in Joel 3:17-21. A lot of what the Old Testament prophets talked about will take place during these 1,000 years.
Some even believe that the Valley of Decision might be where the final judgement of God will be, where the dead without Christ will rise before the Lord Jesus and be judged at the Great White Throne Judgment.
The reference here is to God's decision. What is meant is the situation of God's enemies when they are caught, without possibility of escape, under God's judgment.
The fate which overtakes the wicked again and again in history points up the meaning of this prophecy. It certainly happens that the tables are often turned, that those who take the sword perish by the sword, that whole nations are destroyed in direct consequence of their iniquity. In such instances we see men trapped in the valley of decision. A higher power than their own has overthrown them. An irrevocable decision has been passed, and the decision is against them. TIBExp
Matthew Henry says about what Joel has said, “Here is a challenge to all the enemies of God's people. There is no escaping God's judgments; hardened sinners, in that day of wrath, shall be cut off from all comfort and joy.”
To the wicked it will be a terrible day, but to the righteous it will be a joyful day. What cause have those who possess an interest in Christ, to glory in their Strength and their Redeemer! The acceptable year of the Lord, a day of such great favour to some, will be a day of remarkable vengeance to others: let every one that is out of Christ awake, and flee from the wrath to come.