The Vigil of Pentecost
The first Mass for Pentecost, formerly celebrated during the night, has, like that of Easter, since been anticipated. This great and solemn festival, therefore, begins with the Vigil. In early days the catechumens whom it had not been possible to baptize at Easter received this sacrament at Pentecost, which explains the similarities between the Mass for the Vigil and that for Holy Saturday. It is preceded by the reading of six Prophecies and the blessing of the water in the Baptismal Font, and it is also celebrated at St. John Lateran.
The celebrant and assistant ministers are robed in violet vestments, and the candles on the altar are not lighted until the beginning of Mass, as on Holy Saturday. At the end of the Prophecies the Collect is read, but Flectamus genua is omitted.
Deus, qui in Abrahae famuli tui opere, humano generi obedientiae exempla praebuisti: concede nobis, et nostrae voluntatis pravitatem frangere, et tuorum praeceptorum rectitudinem in omnibus adimplere.
O God, who in the action of Thy servant Abraham hast given to mankind an example of obedience, grant us both to conquer the perverseness of our will and to fulfil in all things Thy righteous commands.
(Collect after the first prophecy)
THE BLESSING OF THE FONT
At the end of the Prophecies the celebrant puts on a violet cope, and while the procession moves towards the font, the Tract Sicut cervus is sung. Then the priest, before blessing the font, says:
Domine, Deus virtutum, qui collapsa reparas, et reparata conservas: auge populos in tui nominis sanctificatione renovandos; ut omnes, qui sacro baptismate diluuntur, tua semper inspiratione dirigantur.
O Lord, God of hosts, who dost restore what is fallen and preserves! what Thou hast restored, increase the number of those to be renewed in Thy holy name; that all who are washed in holy baptism may ever be guided by Thy holy inspiration.
Mindful of the fact that in the beginning the Spirit of God moved over the waters and made them fruitful, the Liturgy asks God to bless the water in the Baptismal Font, out of which will arise a purely heavenly race. The officiating priest then plunges the Paschal candle three several times in the water, for it is by Christ, whom the candle typifies, that the power of the Holy Ghost, by which our souls are enlightened, is infused into them.
THE LITANY OF THE SAINTS
As on Holy Saturday. Where there is no Font, the Litany begins after the Prophecies and Collects. At Peccatores, Te rogamus audi nos, the priest and his assistants go to the sacristy and put on red vestments, and the candles are lit on the altar. At the end of the Litany the Kyrie eleison is solemnly sung, without Introit, like on Holy Saturday. At the Gloria, the bells are also rung and the organ begins being played.
MASS FOR THE VIGIL OF PENTECOST
After having been baptized "in water and in the Holy Ghost" the neophytes were confirmed. All through the Mass there are references these two sacraments, showing how the Holy Ghost enters into our souls and the effect He produces in them.
Praesta, quaesumus, omnipotens Deus: ut claritatis tuae super nos splendor effulgeat; et lux tuae lucis corda eorum, qui per gratiam tuam renati sunt, Sancti Spiritus illustratione confirmet.
Grant, we beseech Thee, O almighty God, that the brightness of Thy glory may shine forth upon us; and the light of Thy light by the illumination of the Holy Ghost, may confirm the hearts of those who have been born again by Thy grace.
Continuation of the holy Gospel according to St. John.
At that time Jesus said to His disciples : If you love Me, keep My commandments. And I will ask the Father, and He shall give you another Paraclete, that He may abide with you for ever, the Spirit of truth, whom the world cannot receive, because it seeth Him not, nor knoweth Him. But you shall know Him; because He shall abide with you and shall be in you. I will not leave you orphans: I will come to you. Yet a little while, and the world seeth Me no more. But you see Me; because I live, and you shall live. In that day you shall know that I am in My Father, and you in Me, and I in you. He that hath My commandments and keepeth them, he it is that loveth Me. And he that loveth Me shall be loved of My Father: and I will love him, and will manifest Myself to him.
(St John 14:15-21)
Catholic Encyclopaedia on Pentecost: http://www.newadvent.org/cathen/15614b.htm