What does Acts 2:17 mean?
Peter and a group of about 120 disciples are in Jerusalem and have just received the Holy Spirit (Acts 2:1–4). The Holy Spirit enables the disciples to speak in different languages. A large number of Jews from all over the Roman Empire, in Jerusalem to celebrate Pentecost, are puzzled about how these Galileans can speak their native languages and thus communicate with such a diverse crowd so personally (Acts 2:8). Peter shows how this event is related to Old Testament prophecy, specifically Joel 2:28–32. Acts 2:17 quotes Joel 2:28.In the book of Joel, God uses the devastation of a locust swarm as a metaphor for how He will judge Judah if they don't repent. If they do repent, He will pull away His judgment and give them signs that He has done so. A primary sign is that He will "pour out [His] Spirit on all flesh." The very morning described earlier in the book of Acts, the Holy Spirit came down to dwell in the Jesus-followers, just as Jesus promised He would (John 14:15–17). For Jesus-followers, the Holy Spirit will reveal to them the truth and the "things that are to come" (John 16:13). To unbelievers, He will "convict the world concerning sin and righteousness and judgment" (John 16:8).
This very moment is proof. The Holy Spirit is guiding Peter into the truth of Old Testament prophecy, something the disciples were not very good at during Jesus' ministry. And He is guiding Peter's audience into repentance (Acts 2:37–41).
Throughout the early years of the church, this verse continues to be proven. Philip the evangelist's daughters are prophets (Acts 21:8–9). Paul sees a vision of a man inviting him to Macedonia (Acts 16:9). Agabus prophesies a great famine (Acts 11:28) and Paul's impending arrest (Acts 21:10–11). Cornelius, an unsaved Gentile described as "a devout man who feared God" (Acts 10:2), sees an angel in a vision who tells him to send for Peter; Peter shares the gospel and Cornelius and his family accept Christ and receive the Holy Spirit (Acts 10).
The language is poetic, which is typical for a book of prophecy in the Bible. God doesn't mean to say that only sons and daughters will prophesy, or that young men will only receive messages while they're awake and only old men will hear from God when they're sleeping. The verse is in a synthetic parallel format and just means that "people" will receive "messages" from God in various ways.
One of the great questions of the church is, are these visions and prophesies for the early church age, or are they meant to continue through to the end times? It's true that seekers and believers around the world have seen visions that led them closer to Jesus. But the supernatural messages seem to have decreased greatly since the church compiled the canon of the books that belong in the New Testament. Scripture is the primary way that God communicates with the world today.
