On Pentecost Sunday, we commemorate the coming of the Holy Spirit upon the Apostles and other followers of Jesus Christ. From a historical point of view, Pentecost is the day on which the Church was started. From a spiritual perspective, Pentecost is that day when the Church received power — since the Holy Spirit brings the Church into existence, empowers it, and enlivens it. Thus, Pentecost is the Church’s birthday.