This is what Joel spoke about

When Peter stood up on the day of Pentecost to preach the first Christian sermon, he had to both refute and explain. One portion of the crowd was asking for understanding and the other part was mocking. In an attempt to address both segments of the crowd, Peter refuted the skeptics with a common sense argument and he explained the meaning of Pentecost by making an appeal to Joel 2. The heart of Peter's message is that Pentecost means the Spirit has been poured out and the messianic age of salvation has arrived.