This Sunday is the greatest feast of the Church save Easter itself. It is the day on which we remember the Holy Spirit's descent upon the Apostles and the Virgin Mary at Pentecost.
In the Old Testament, Pentecost was originally a Jewish holy day that celebrated the harvest, in which the Jewish people gave to God the first fruits of their harvests. However, over time, the Jewish people began to connect the celebration of Pentecost to a celebration of the giving of the Law to Moses. Christian Pentecost is a fulfillment of this, because the New Law is the Law inscribed upon our hearts by the Holy Spirit - it is itself the grace of the Holy Spirit, as St. Thomas Aquinas points out. Also, many see this as the birth of the Church, since it is on this day that the apostles - filled with the fire of the Holy Spirit - began to preach the Gospel of Our Lord Jesus Christ.
Ant. The Spirit of the Lord has filled the whole world, alleluia; and that which contains all things has knowledge of the voice, alleluia, alleluia, alleluia.
V. Let God arise, and let His enemies be scattered; and let them that hate Him flee from before His face.
V. Glory be...
V. Come, Holy Spirit, send forth the heavenly radiance of Your light.
V. Come, Father of the poor. Come, Giver of gifts. Come, Light of the heart.
V. Greatest Comforter, sweet Guest of the soul, Sweet consolation!
V. O Rest in labor, O Temperance in heat, O Solace in tears,
V. O most blessed Light, fill the inmost heart of Your faithful.
V. Without Your spirit, there is nothing in man, nothing that is not harmful.
V. Cleanse that which is unclean; water that which is dry; heal that which is wounded.
V. Bend that which is rigid; inflame that which is frigid; rule that which has deviated.
V. Grant to Your faithful who trust in You, the sevenfold gifts.
V. Grant the merit of virtue; grant the deliverance of salvation; grant eternal joy. Amen. Alleluia.
Ant. Confirm, O God, what Thou hast wrought in us; from Thy temple. which is in Jerusalem, kings shall offer presents to Thee, alleluia.
Suddenly there came a sound from heaven, as of a mighty wind coming where they were sitting, alleluia; and they were all filled with the Holy Spirit, speaking the great things of God, alleluia, alleluia.
Veni Creator Spiritus:
I have decided that beyond the propers of the Mass posted above that this post should contain the Veni Creator Spiritus which is a hymn to which many have a great devotion. This hymn is an ancient hymn which is traditionally sung by the Church at Vespers during the Octave of Pentecost. The devotion to this hymn however, is encouraged even for those who do not pray the Divine Office, and this can be seen first and foremost in that the Church grants a plenary indulgence to those who pray this hymn on the feast of Pentecost (with the usual conditions).
V. Drive far from us the foe we dread,
And grant us Thy true peace instead;
So shall we not, with Thee for guide,
Turn from the path of life aside.
V. O, may Thy grace on us bestow
The Father and the Son to know,
And Thee, through endless times confessed,
Of both the eternal Spirit blest.
V. All glory, while the ages run,
Be to the Father and the Son
Who rose from death; the same to Thee,
O Holy Ghost, eternally. Amen.
V. Come, O Creator, Spirit blest,
And in our souls take up Thy rest,
Come with Thy grace and heavenly aid,
To fill the hearts which Thou hast made.
V. Great Paraclete, to Thee we cry,
O highest Gift of God most high,
O Fount of life, O Fire, O Love,
And sweet anointing from above.
V. Thou in Thy sevenfold gifts art known,
The Finger of God's Hand we own;
The promise of the Father, Thou,
Who dost the tongue with power endow!
V. Kindle our senses from above,
And make our hearts overflow with love;
With patience firm and virtue high
The weakness of our flesh supply.