What does Acts 2:15 mean?

The evangelistic and apologetic speeches recorded in Acts include three from Peter (Acts 2:14–41; 3:12–26; 10:34–43), one from Stephen (Acts 7:2–53), and several from Paul. One notable characteristic of all of them is that they attempt to fully explain the questions and concerns of the audience, addressing what is going on right then and there.

Here, Peter is answering the charge that the Jesus-followers are drunk (Acts 2:13). In fact, they are filled with the Holy Spirit and speaking in foreign languages (Acts 2:1–4). But those without "ears to hear" (Matthew 11:15) apparently just hear gibberish. Peter goes on to explain that it's only nine in the morning (Acts 2:15). Jews haven't even started eating for the feast, yet. The claim they are drunk is an ad hominem attack: a specious criticism against the character of the speakers instead of a logical response to their argument.

But the fact that Peter addresses the attack says something important about evangelism. This is a large crowd, but only part of the 900,000-or-so visitors in Jerusalem. It's very possible that those who assume they're hearing gibberish, not a language, are resisting the Holy Spirit. But 3,000 others (Acts 2:41) are chosen, and many of them heard these accusations. By proving the charges wrong, Peter has removed a stumbling block to the gospel—not for the accusers but for the other audience members.

Apologetics is the art of defending the Christian faith. Evangelism is the transmission of the message that Jesus saves. It's been said that evangelism is exclusively for non-believers, to bring them to the faith, but apologetics can also apply to believers, helping to keep their faith strong. Peter proves that apologetics can be important for pre-believers, as well. He answers a small problem in a decisive way and clears the air for the bigger message. He also proves that he is paying attention to the concerns and questions around him. That makes it much easier for the crowd to listen to and accept his words.