When Peter quotes from Joel, he quotes 3:1-5 (Hebrew text; the numbering of the English text is a bit different). As you will notice, vv. 19-21 are a part of the same quotation. This puts us in a dilemma. Verses 19-20 certainly were not fulfilled literally on the day of Pentecost—the sun was not darkened, the moon did not turn to blood. Further, v. 20 seems to indicate that such things would happen just before the great day of the Lord came. This ought to give us our first clue about how Peter is using the Old Testament.
In verse 16 he introduces the passage by saying, “This is that which was spoken by the prophet Joel.” Our options at this point seem to be as follows: (1) this prophecy was completely fulfilled on the day of Pentecost, though only part of it was literal and part of it was not; (2) this prophecy was not fulfilled at all on the day of Pentecost, but Peter was speaking analogically—as if to say, “Joel talked about something very similar to this; therefore, what is happening is the Lord’s doing”; or (3) this prophecy was partially fulfilled on the day of Pentecost (and there are variations to that answer too).
The problems with the first view are: (a) the reference to the day of the Lord (v 20) clearly locates the fulfillment of the prophecy in the time just prior to Jesus’ return—hence, either Peter was wrong in seeing it fulfilled on the day of Pentecost (!) or else this interpretation is wrong; (b) to mix literal fulfillment with non-literal in the manner done here is, I think, unparalleled elsewhere in fulfillment texts, making this view rather suspicious (further, it is doubtful that even v. 17 was fulfilled completely literally, for we have no evidence that either women or old men prophesied on that day; it was most likely the apostles alone who spoke in tongues and prophesied).
The problem with the second view is that Peter says, “This IS that...” He doesn’t say “This is LIKE that.” I do not know any introductory formulas in the New Testament which formally make such an equation and which, in reality, are only analogical.
So what about the third view? Is it possible that this was partially fulfilled—and if so, in what way? I believe this is the correct view of the text, though some feel uncomfortable about it, for they believe that prophecy has only one final fulfillment. But more and more scholars are coming to recognize that biblical prophecy and its fulfillment does not fit our western way of viewing things. In the Olivet Discourse, for example, Jesus mixes in the destruction of Jerusalem and the tribulation before his second coming, without clearly separating them. When Jerusalem was destroyed, this was a partial fulfillment of his words—kind of a down payment of future fulfillment. When John speaks about the antichrist coming, he also notes that many antichrists are already in the world. Partial fulfillment again.
Here’s a crass analogy: a gangster takes a baseball bat and destroys a grocery store because the owner would not pay for protection. Such action would be viewed as much as a warning of bodily harm as actual damage to the property. In effect, it is as if the thug were saying, “I’ll do the same to you next time if you don’t pay.” So it is with biblical prophecy. Partial fulfillment indicates that more is to come.
So, back to Acts 2:17. The key element that was fulfilled on the day of Pentecost was the coming of the Spirit. The new covenant had been inaugurated; the kingdom was now, in some sense, here. Notice the repeated mention of the Spirit throughout the prophecy. All this was designed to show that the old covenant was now done away via Christ’s first coming. Does this mean, then, that all elements of the Joel prophecy needed to find their fulfillment on that day? Not at all, if we are to see other biblical prophecy fulfillments as a guide. Does it mean that there would be a steady stream of fulfillment until the whole thing culminated in the day of the Lord? Again, no—and again, due to the analogy of other biblical prophecy fulfillments (otherwise, we would have to say that ‘wars and rumors of wars’ continued to steadily increase from AD 70 until the present era).
So where does this put us with reference to the continuation of the sign gifts? I would argue two things: (1) The key element that Peter was tapping into in Joel’s prophecy was the gift of the Spirit as evidence that the new covenant had been inaugurated. This is a point that the rest of the NT authors are united on and still continues to this day. (2) The biblical motif of multiple fulfillment normally implies that certain parts of the prophecy will not be fulfilled at all until the final fulfillment (in this case, the astronomical alterations), others would be partially and temporarily fulfilled, but would not form an unbroken stream from then until now (in this case, I believe the prophesying fits that description), and the main point of the prophecy would have an abiding significance (in this case, the gift of the Spirit to those who embrace Christ as Savior).