This seems to be an umbrella-use of the verb ‘to prophecy’. As Luther put it, ‘prophesying, visions and dreams are all one thing’. That is, the universal gift (the Spirit) will lead to a universal ministry (prophecy). Yet the promise is surprising because elsewhere in Acts- and in the New Testament generally – only some are called to be prophets. How then shall we understand a universal prophetic ministry? If in its essence prophecy is God speaking, God making himself known by his Word, then certainly the Old Testament expectation was that in New Covenant days the knowledge of God would be universal, and the New Testament authors declare that this has been fulfilled through Christ (Jer 31:34; 1 Thess 4:9; 1 John 2:27). In this sense all God’s people are now prophets, just as all are also priests and kings. So Luther understood prophecy here as ‘the knowledge of God through Christ which the Holy Spirit kindles and makes to burn through the word of the gospel’, while Calvin wrote that it ‘signifies simply the rare and excellent gift of understanding’. In fact, it is this universal knowledge of God through Christ by the Spirit which is the foundation of the universal commission to witness (Acts 1:8). Because we know him, we must make him known.
John Stott, The Message of Acts, 74.