NOTES for Act 2:14-21
Speaking to those who had gathered, Peter first of all defends the apostles from the accusation of drunkenness. This was vitally necessary in order to justify the seriousness of the apostolic preaching. Unfortunately, in our time Peter's argument that people cannot be drunk because it is still too early would no longer work: customs have changed greatly, and lovers of alcohol get drunk at any time... But whatever opponents may say, both those of that day and later ones, Christianity is inseparable from sobriety, understood more broadly than abstaining from alcohol: faith gives the most sober possible view of reality.
Noting the similarity between what is happening and what was foretold in Joel's prophecy, Peter relies on Old Testament prophecy not because he wants to drag a proof from ancient books into current events by force. Yes, he is addressing people who need argument based on the books of the Old Testament, but the whole point is that Peter really does see that the Old Testament prophecies are being truly disclosed before the eyes of those gathered. The more we compare the Old and New Testaments, the more we will be able to see their interconnection.