For a brief Old Testament book concerned primarily with a swarm of locusts, Joel contains some startling passages of prophecy that will bear fruit in the New Testament!
After a detailed description of the "army" of locusts, Joel encourages the people to turn to the Lord in the hope that He will relent and have compassion on them. Joel shares the good news that the Lord will end the plague and restore the land. He promises that God will send the rains and that "the threshing floors shall be full of grain, the vats shall overflow with wine and oil" (vs. 24). It sounds like a happy ending for the people of God (vs. 25-27).
But Joel is really just getting started. In verses 28 and 29 we hear this gem which will be cited by the apostle Peter in Acts 2: "Then afterward I will pour out my spirit on all flesh; your sons and your daughters shall prophesy, your old men shall dream dreams, and your young men shall see visions. Even on the male and female slaves, in those days, I will pour out my spirit." What Joel promised in terms of an outpouring of the Holy Spirit, the early Church recognized as coming to fruition on the day of Pentecost.
In addition, Joel makes a staggering theological claim: "Then everyone who calls on the name of the Lord shall be saved" (vs. 32). In an era where salvation came through slavish obedience to the covenantal laws of obedience, sacrifice, and ritual cleanliness, Joel revealed that God's heart is actually most responsive to those who cry out to Him. Not included in his observation are commands regarding circumcision or atonement offerings. Joel's words apparently left a powerful imprint. This formulation of "everyone who calls on the name of the Lord shall be saved" is picked up in the New Testament twice. It can be found in Acts 2:21 on the lips of Peter and Romans 10:13 from the pen of Paul.
The prophet Joel plants some amazing seeds that will find their flowering when seen through the light of the grace of Christ and the coming of the Holy Spirit.