Today is usually recognised as being the birthday of the Church. Pentecost Sunday is celebrated on the 50th day, the seventh Sunday, from Easter Sunday. It commemorates the descent of the Holy Spirit upon the Apostles and other followers of Jesus Christ while they were in Jerusalem celebrating the Jewish festival of the Feast of Weeks.
It is the day when the apostles came out of their locked room and began to preach and speak with those who had gathered in Jerusalem at that time. The church was born, and the Spirit of God continues to spread and empower Christ