The Holy Spirit was abundantly poured out upon the apostles, but other members of the Church of Christ are given the Holy Spirit through repentance, Baptism, and the other Sacraments. The event of the descent of the Holy Spirit upon the apostles is very important for the Church of Christ. This day is the day of the true foundation of the Christian Church, or the Christian society of those saved in Christ.
At that time, the Holy Spirit came into the world—the other Comforter besides the Lord Jesus Christ, equally powerful and co-eternal with Him and God the Father. From this event the Holy Spirit has spread the proclamation of the Gospel throughout the world through the holy apostles and their holy successors, and through this preaching has grown and expanded the Church throughout the universe, and has made wise the holy fathers to overthrow all the delusions of heretics, to compile the Divinely-wise Scriptures, and to preserve the faith holy and pure to our day.
The Holy Spirit has made an innumerable multitude of God-pleasing people holy, and glorified them with miracles and incorrupt relics, and works towards the salvation of us all, even until our day.
Everything that we have now in the Holy Church—all of its spiritual riches, all the grace coming from its prayers and Sacraments—all of it originates from the holy day of Pentecost.
That is why the present feast is so joyous and why we have a special feeling this day. The grace of the Holy Spirit especially and ineffably fills the very air and all of us today, allowing none to have just an everyday feeling.
That is why this feast is called the feast of the Holy Trinity, with the entire Holy Trinity participating perceptibly in our salvation from this day: the Father, Who sent the Son, the Son, Who came into the world and suffered and redeemed the whole of mankind, and the Holy Spirit, the Comforter, Who illuminated the holy apostles on the day of holy Pentecost.
Today, more than other days, we are able to understand appreciate what a treasure we have, honoring God, precisely in worshiping the Trinity. The Christian faith differs from other faiths precisely in that we honor the One God in Three Persons.
Let us turn to God the Holy Spirit with love and prayer with the words of the Church’s prayer: “O Heavenly King, the Comforter, the Spirit of Truth, Who art everywhere present and fillest all things, come and abide in us, and cleanse us from every impurity, and save us!” Amen.
From the book Homilies by Archimandrite Kirill (Pavlov), published by the Holy Trinity-St. Sergius Lavra in 2003