Pentecost comes fifty days after Easter and Jesus' ascension to heaven. Mary and the Apostles were in Jerusalem celebrating the Jewish harvest feast called Shavuot (Feast of Weeks) which gives thanksgiving to the first fruits of the wheat harvest, but is also associated with a remembrance of the Law given by God to Moses on Mount Sinai.
As Jesus had promised them, the Holy Spirit descended upon Mary and the Apostles as tongues of fire and sounded like a great wind. The Apostles began speaking in foreign tongues, which allowed them to proclaim Jesus' resurrection in many different languages. Peter and the Apostles went out that day and baptized 3,000 people, thus the Church was born and Peter became the first pope of the Catholic Church.
So on this day, the Catholic Church was born, but more importantly the Holy Spirit bestowed the following gifts upon each of us: wisdom, understanding, counsel, fortitude, knowledge, piety, and fear of the Lord.
We also receive the fruits of the Holy Spirit: charity/love, joy, peace, patience, kindness, goodness, generosity, gentleness, faithfulness, modesty, self-control, and chastity.
Our prayer for you as you celebrate the Holy Spirit in each of us:
May we come to trust the Word of God in our heart, to speak it with courage, to follow it faithfully and to fan it to flame in others.