After all, he was a fisherman, not an orator. Truth be known, Peter had no business being up there in front of ANY folks, much less all those. There is one thing more that must be noted about this gift of the Spirit that Jesus gave. That is why fire fascinates us so. It can do more in minutes than a great host could do in a lifetime.
Fire fascinates because fire has such power.
Peter knew that power. And that preaching had such power, the power of the FIRE, that the church grew from 120 to 3,000 in just one day. He probably did not understand it. I doubt that any of them did. The folks who heard him did not, especially when they heard the message of the disciples in the languages of their own homelands.