As I posted previously in my post entitled "Vigil of Pentecost: Fast and Abstinence":
Today's preparation should not be underestimated. Catholics should fast and partially abstain from meat today (as per 1962 rubrics) in order to better conform themselves to celebrate this High Holy Day of Pentecost.
As the missal's opening section states before the Propers:
The feast of Whitsun [another name for Pentecost] is as ancient as that of Easter, and First Vespers on the Saturday following begins the liturgical season called Season after Pentecost. The Ascension of God's Son, Our Lord Jesus Christ, to Heaven did not leave us abandoned and helpless. By the Divine Will, the Third Person of the Trinity is to be the soul and guiding light of Christ's Mystical Body.
INTROIT Ezech. 36:23-24, 25-26
When I shall be sanctified in you, I will gather you together out of all the countries; and I will pour upon you clean water and you shall be cleansed from all your filthiness, and I will give you a new spirit, alleluia, alleluia! Ps. 33:2. I will bless the Lord at all times; His praise shall ever be in my mouth. V. Glory be . . .
Let the brightness of Your glory shine upon us, Almighty God, so that the Holy Spirit, light of Your light, may strengthen the hearts of those who are reborn in Your grace. Through Our Lord . . .
Now it was while Apollo was at Corinth, that Paul, having passed through the upper coasts, came to Ephesus and found certain disciples. And he said to them: "Have you received the Holy Ghost since ye believed?" But they said to him: "We have not so much as heard whether there be a Holy Ghost." And he said: "In what then were you baptized?" Who said: "In John's baptism." Then Paul said: "John baptized the people with the baptism of penance saying: That they should believe in him, who was to come after him, that is to say, in Jesus." Having heard these things, they were baptized in the name of the Lord Jesus. And when Paul had imposed his hands on them, the Holy Ghost came upon them: and they spoke with tongues and prophesied. And all the men were about twelve. And entering into the synagogue, he spoke boldly for the space of three months, disputing and exhorting concerning the kingdom of God.
Alleluia! V. Ps. 106:1. Praise the Lord, for He is good, for His mercy endures forever.
TRACT Ps. 116:1-2
Praise the Lord, all you nations; praise Him in unison, all you peoples!
V. For His mercy is steadfast towards us, and the truth of the Lord endures forever.
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."
Send forth Your Spirit, and they shall be created, and You shall renew the face of the earth. May the glory of the Lord endure forever, alleluia!
Bless our offering, O Lord, and cleanse our hearts by the light of the Holy Spirit. Through Our Lord . . .
On the last day of the feast, Jesus said, "He who believes in Me, from within him there shall flow rivers of living water." He said this of the Spirit, whom they who believed in Him were to receive, alleluia, alleluia!
May the coming of the Holy Spirit cleanse our hearts, and, as a heavenly dew, water them to bring forth good fruit. Through Our Lord . . .