The book of Acts of the holy Apostles, dealing with the story of the first Christians at the time of early spreading of Christianity starts with the words of Christ He said before His Ascension, “And eating together with them, he commanded them, that they should not depart from Jerusalem, but should wait for the promise of the Father, which you have heard (saith he) by my mouth. For John indeed baptized with water, but you shall be baptized with the Holy Ghost, not many days hence.”(Acts 1: 4-5)

After the Saviour went to Heaven, His disciples were full of joy and were waiting for the descent of the Comforter – the Lord Holy Spirit, the third person of the Holy Trinity. At last, the tenth day after the Ascension and the fiftieth after Passover came. This was the day of Pentecost – one of the three Great Feasts of the Old Testament. The Jews made remembrance of getting the ten Commandments from God through Moses on Mount of Sinai on that day. The Jews from all countries came to Jerusalem that day.

“And when the days of Pentecost were accomplished, they were all together in one place: And suddenly there came a sound from heaven, as of a mighty wind coming, and it filled the whole house where they were sitting. And there appeared to them parted tongues as it were of fire, and it sat upon every one of them: And they were all filled with the Holy Ghost, and they began to speak with diverse tongues, according as the Holy Ghost gave them to speak.” (Acts 2: 1-4)

The noise attracted many Jews to the house where the Apostles were sitting. When the disciples saw the people coming, they rejoiced and exalted God with prayers of gratitude and came to the people gathered in front of the house. Everyone was shocked: the Apostles, being common people, started speaking foreign tongues at once! There were people of various nations, and every one of them could hear the exuberant narration about the great actions of God in their own tongue. The people were astounded, they could not imagine anything of that kind and they said to one another, “What does that mean?” Then Apostle Peter came forth and exclaimed, “Men of Galilee and all of you who are in Jerusalem! Listen to my words! Jesus the Nazarene lived among us and worked many wonders, but you took Him and nailed Him to the cross and slaughtered Him. But God has raised Him from the dead. He trampled down death and ascended up to Heaven to God the Father and poured down on us His Holy Spirit, Whom you now can witness…”

The feast to commemorate the great event of the descent of the Holy Spirit was established by the Apostles themselves. After this event, they began to celebrate the day of Pentecost yearly and instructed all Christians to do so, “There is the fiftieth day from the first Day of the Lord (Pascha), which is also the tenth day from the Ascension; this day must be a great feast. For it is at the third hour of that day that the Lord sent His Holy Spirit.” (Apostolic Rules). Pentecost, also known as the Day of Ascension of the Holy Spirit has been solemnly celebrated by the Church since the very first days of Christianity. The other name of this feast –Holy Trinity Day – is explained by the fact that the third person of the Holy Trinity was made manifest with the descent of the Holy Spirit onto the Apostles. It is on this day that the Church calls the faithful to worship the Triune God – the Father, and the Son, and the Holy Spirit.

It is customary for our people to decorate the churches and the parishioners’ homes with branches of trees on the day of the descent of the Holy Spirit, mainly with young birch trees and grass and flowers; people hold flowers in their hands when they are in church. This is how the Old Testament Church celebrated Pentecost. Perhaps, the upper chamber of Zion where the Holy Spirit descended onto the Apostles was also decorated with grass. The green branches in our homes make us remember the oaks of Mamre, where Patriarch Abraham had the honour to host God in three Persons in Old Testament times. The well-known icon by St Andrew Rublev portrays this very event.

There is also a feast in honour of the All-Holy, Life-Giving and Almighty Spirit (the Day of the Holy Spirit) on the Monday after Holy Trinity Day.

Extract from the book «Orthodox feasts» by G. Sytenko. Minsk 1995

The Troparion for the feast:

Blessed art Thou O Christ Our God
You have revealed the fishermen as most wise
By sending down upon them the Holy Spirit
Through them You drew the world into Your net
O Lover of Man, Glory to You!

Chrysostom, Archbishop of Vilnius and Lithuania:

It was only on the Day of Pentecost when the Apostles accepted Christ with all their faith and conscience, with all the fullness of their spirit. This was the day when they were baptized with the Holy Spirit. It was since then that the feeble and weak-spirited disciples of Christ were vested with power from above and became daring ministers, not frightened by any threats and torture, and death.

This is why Holy Trinity Day is also called the Birthday of the Church.