(Thanks Priscilla for doing this interesting research!)
Pentecost is the Greek for "the fiftieth" (day after Easter).
A feast of the universal Church which commemorates the Descent of the Holy Spirit upon the Apostles, fifty days after the Resurrection of Christ.
It originated as a Jewish festival fifty days after Passover.
Whitsunday is so called from the white garments which were worn by those who were baptized during the vigil. During the vigil formerly the catechumens who remained from Easter were baptized, consequently the ceremonies on Saturday are similar to those on Holy Saturday.
Whitsunday, as a Christian feast, dates back to the first century, although there is no evidence that it was observed. This is not surprising, for the feast, originally of only one day's duration, fell on a Sunday; besides it was so closely bound up with Easter that it appears to be not much more than the termination of Paschal tide.
The first Pentecost
Pentecost comes from a Jewish harvest festival called Shavuot.
The apostles were celebrating this festival when the Holy Spirit descended on them.
It sounded like a very strong wind, and it looked like tongues of fire.
The apostles then found themselves speaking in foreign languages, inspired by the Holy Spirit, so that everyone from every country understood the Christians inspired message of salvation as if the they were hearing it in their own languages. Thousands were converted by the preaching of Peter and the other apostles.
How it’s celebrated
The Gallic pilgrim gives a detailed account of the solemn manner in which it was observed at Jerusalem. The Apostolic Constitutions say that Pentecost lasts one week, but in the West it was not kept with an octave until at quite a late date. At present it is of equal rank with Easter Sunday.
The office of Pentecost has only one Nocturn during the entire week.
At Terce the "Veni Creator" is sung instead of the usual hymn, because at the third hour the Holy Spirit descended. The Mass has a Sequence, "Veni Sancte Spiritus".
Formerly the law courts did not sit during the entire week, and servile work was forbidden. A Council of Constance (1094) limited this prohibition to the first three days of the week. The Sabbath rest of Tuesday was abolished in 1771, and in many missionary territories also that of Monday; the latter was abrogated for the entire Church by Pius X in 1911.
In Italy it was customary to scatter rose leaves from the ceiling of the churches to recall the miracle of the fiery tongues; hence in Sicily and elsewhere in Italy Whitsunday is called Pascha rosatum. The Italian name Pascha rossa comes from the red colours of the vestments used on Whitsunday.
In France it was customary to blow trumpets during Divine service, to recall the sound of the mighty wind which accompanied the Descent of the Holy Ghost.
In England the gentry amused themselves with horse races. The Whitsun Ales or merrymakings are almost wholly obsolete in England. At these ales the Whitsun plays were performed.
At Vespers of Pentecost in the Oriental Churches the extraordinary service of genuflexion, accompanied by long poetical prayers and psalms, takes place.
On Pentecost the Russians carry flowers and green branches in their hands.
Pentecost Symbols
The symbols of Pentecost are those of the Holy Spirit and include flames, wind, the breath of God and a Dove.
Seven Gifts of the Holy Spirit
Wisdom
Understanding
Counsel
Fortitude
Knowledge
Piety
Fear of the Lord
The moral life of Christians is sustained by the gifts of the Holy Spirit, according to the Catechism of the Catholic Church. These are permanent dispositions which make man docile in following the promptings of the Holy Spirit
