At the first Pentecost, Peter, Mary, the apostles and their followers were gathered in the upper room in Jerusalem, where Jews from all over the world were still in town celebrating the end of Passover. A great wind blew and a flame appeared as a tongue of fire, which split itself into individual flames above the heads of all those present. The Holy Spirit came upon those gathered and each began to speak in tongues. Despite the fact many had no common language, they were perfectly able to understand one another.
As those in the room went out among the crowd to spread the Good News, some accused those speaking in tongues of being intoxicated. Peter explained to the crowd that this was the work of the Holy Spirit, as prophesied in Scripture, and began preaching to them. Peter then called on those present – about 3,000 people – to be baptized. That moment firmly established Peter as the leader of the faith – the “rock” Jesus had previously told him he would become – and is known as the birthday of the Church.