Pentecost is the feast celebrating the descent of the Holy Spirit upon the apostles and the Blessed Virgin Mary, fifty days after Easter. It is often called the 'birthday of the Church' because it marks the moment when the apostles, empowered by the Spirit, began publicly proclaiming the Gospel. The event is described in Acts 2:1-13: a sound like a rushing wind filled the room, tongues of fire appeared over each person, and the apostles began speaking in different languages, understood by the diverse crowd gathered in Jerusalem. Peter then delivered his first sermon, and about three thousand people were baptized that day. In the liturgical calendar, Pentecost marks the end of the Easter season. The liturgical color is red, symbolizing the fire of the Holy Spirit. The feast has Old Testament roots in the Jewish feast of Shavuot (Feast of Weeks), which celebrated the giving of the Law on Mount Sinai — fittingly, the Holy Spirit now writes God's law on human hearts (Jeremiah 31:33). The gifts of the Holy Spirit — wisdom, understanding, counsel, fortitude, knowledge, piety, and fear of the Lord — are particularly celebrated on this day.