Pentecost Sunday - The Day of the Holy Trinity
This coming Sunday marks the end of the cycle that began with Great Lent. The weeks of Lent served to prepare us for the Feast of Pascha. But Pascha itself served to open the world to the Feast of Pentecost.
On that day, 50 days after Pascha ("Pentecost" means "50"), we read in the Book of Acts how the Holy Spirit descended on the disciples and the entire fledgling Church in Jerusalem. It gave them power and understanding to preach the news of what Christ's death and resurrection means for the whole creation. That day, several thousand believers were added to the Church.
The feast is also known as the "Day of the Holy Trinity," in that it was an occasion in which the fullness of the three divine persons is made known in the life of the Church. Christ promised that the Father would send a "Comforter" (the Holy Spirit) who would both make God known, but also dwell in the lives of all believers.
The Holy Trinity is beyond our understanding, but Pentecost pulls back the veil and allows us to glimpse the truth in a fuller manner.
In the Church, the day is marked by the "Kneeling Vespers" of Pentecost. It is the first time we kneel in Church for prayers following Pascha (hence the nickname). That service has within it petitions for the whole world and all of humanity, both the living and the departed. It is, without a doubt, the boldest expression of the goodness of God and our trust in that goodness.
On the day before (Saturday morning), there is the last of the "Soul Saturdays" in which prayers for the departed are offered.