Sunday, May 19th is the Solemnity of Pentecost. The Solemnity is celebrated on the 50th and final day of the Easter season.
On Pentecost, the Holy Spirit transformed fearful apostles into courageous witnesses to Christ and to baptize those who believed. Those who were baptized created communities to share their new faith in Christ with one another. Pentecost is the birthday of the Church and from this the age of the Church began.