In the first half of the book of Joel we read of Joel's call to repentance and of the people's response. In this last half of the book, we read of God's words and His response to the people's repentance (2:18-3:21). In His goodness and mercy, God would stop the destruction of the locust (the northern army) by miraculously causing them to die. With millions of locusts dead, there would be a stench in the air (2:20), but it would serve to remind the people of the salvation and omnipotence of their God. Then the Lord would immediately restore all that the locusts had destroyed and bless them with plentiful rains and bountiful harvests. These blessings would show the people that the Lord is in their midst (2:27). It will be only then, among the repentant people, that there will be an outpouring of God's Holy Spirit (2:28-29). This is the ultimate blessing.
Joel prophesied that the Spirit of God would be poured out on "all flesh" (mankind), without distinction of sex, age, or social status. The Apostle Peter explained that the fulfillment of this prophecy began on the Day of Pentecost, and it also included no distinction of nationality. Believing Gentiles, as well as believing Jews, were filled with the Holy Spirit (Acts 2:16-21; 10:45-46). The final fulfillment of Joel's prophecy, however, is still to be realized in the future with the complete victory of the kingdom of the Lord Jesus Christ.
The Millenial Kingdom of the Messiah will be preceeded by "wonders in the heavens and in the earth" (2:30). "Blood and fire and pillars of smoke" signify bloody wars, destruction, and burning cities. The sun will lose its light and the moon will in some way become a red colour. These extraordinary happenings will be portents (prophetic warnings) that will mark the nearness of "the great and terrible day of the Lord". But the Lord God has a plan of salvation, for "whoever calls on the name of the Lord shall be saved" (2:32). Here Joel sees a saving faith that does not come from religious practices or obedience to the law. "The name" Joel refers to is the personal name of God that is so revered that it is never even pronounced by the Jews. In this light, it might seem strange for Joel to urge people to call on that name (no one really even knew how to pronounce it). These events, however, are to occur in the last days, after the outpouring of the Spirit that followed the redemptive work and ascension of the Lord Jesus. By this time everyone whom the Lord calls will know that wonderful name — the name is "Jesus" (Rom. 10:12-13; Acts 4:12). Joel calls all those who will be saved (delivered from death) "the remnant whom the Lord calls". The New Testament sees them as the elect of God (Rom. 9:27; 11:5) — a part of the Church of the Lord Jesus Christ.
In the final chapter of Joel, we see the judgment of the nations. It is to take place in "the valley of Jehoshaphat" (3:2,12), an unknown geographical location. This valley, however, may simply be symbolic, for its name means, "the valley where the Lord judges". Joel prophesies concerning the judgment of the nations known to him which persecuted God's people. The way they have treated God's people is the way God will treat them (3:4, 7). He also prophesies of the certainty of judgment upon other nations ("multitudes") unknown to him (3:14). This time of judgment is to be feared by all those who have not called upon the name of Jesus in faith. But for those who have called upon Him, there is nothing to fear; they will find strength and shelter in the Lord. Because of this time of divine judgment and vindication, the Lord will ensure the safety and survival of His people. In contrast to the desolation of the sinful, wicked world, Joel picturesquely describes the wonderful eternal future for the people of the Lord. At that time, waters of life will flow from the throne of God (E/ek. 47:1; Rev. 22:1), and since His presence will forever be there, it will be an eternal era of peace, prosperity, victory, satisfaction, and holiness (3:18-21).