First Reading:

Acts 2: 1-11 [Year A,B,C]
When the day of Pentecost had come, they were all together in one place. And suddenly a sound came from heaven like the rush of a mighty wind, and it filled all the house where they were sitting. And there appeared to them tongues as of fire, distributed and resting on each one of them. And they were all filled with the Holy Spirit and began to speak in other tongues, as the Spirit gave them utterance.

Now there were dwelling in Jerusalem Jews, devout men from every nation under heaven. And at this sound the multitude came together, and they were bewildered, because each one heard them speaking in his own language. And they were amazed and wondered, saying, "Are not all these who are speaking Galileans? And how is it that we hear, each of us in his own native language? Parthians and Medes and Elamites and residents of Mesopotamia, Judea and Cappadocia, Pontus and Asia, Phrygia and Pamphylia, Egypt and the parts of Libya belonging to Cyrene, and visitors from Rome, both Jews and proselytes, Cretans and Arabians, we hear them telling in our own tongues the mighty works of God."

Second Reading:
1 Corinthians 12:3b-7, 12-13 [Year A,B,C]
No one can say "Jesus is Lord" except by the Holy Spirit.

Now there are varieties of gifts, but the same Spirit; and there are varieties of service, but the same Lord; and there are varieties of working, but it is the same God who inspires them all in every one. To each is given the manifestation of the Spirit for the common good.

For just as the body is one and has many members, and all the members of the body, though many, are one body, so it is with Christ. For by one Spirit we were all baptized into one body - Jews or Greeks, slaves or free - and all were made to drink of one Spirit.

or

Galatians 5:16-25 [Year B]

But I say, walk by the Spirit, and do not gratify the desires of the flesh. For the desires of the flesh are against the Spirit, and the desires of the Spirit are against the flesh; for these are opposed to each other, to prevent you from doing what you would. But if you are led by the Spirit you are not under the law. Now the works of the flesh are plain: fornication, impurity, licentiousness, idolatry, sorcery, enmity, strife, jealousy, anger, selfishness, dissension, party spirit, envy, drunkenness, carousing, and the like. I warn you, as I warned you before, that those who do such things shall not inherit the kingdom of God. But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such there is no law. And those who belong to Christ Jesus have crucified the flesh with its passions and desires. If we live by the Spirit, let us also walk by the Spirit.

Romans 8:8-17 [Year C]

Those who are in the flesh cannot please God.

But you are not in the flesh, you are in the Spirit, if in fact the Spirit of God dwells in you. Any one who does not have the Spirit of Christ does not belong to him. But if Christ is in you, although your bodies are dead because of sin, your spirits are alive because of righteousness. If the Spirit of him who raised Jesus from the dead dwells in you, he who raised Christ Jesus from the dead will give life to your mortal bodies also through his Spirit which dwells in you.

So then, brethren, we are debtors, not to the flesh, to live according to the flesh-- for if you live according to the flesh you will die, but if by the Spirit you put to death the deeds of the body you will live. For all who are led by the Spirit of God are sons of God. For you did not receive the spirit of slavery to fall back into fear, but you have received the spirit of sonship. When we cry, “Abba! Father!” it is the Spirit himself bearing witness with our spirit that we are children of God, and if children, then heirs, heirs of God and fellow heirs with Christ, provided we suffer with him in order that we may also be glorified with him.

Gospel Reading:
John 20:19-23 [Year A,B,C]
On the evening of that day, the first day of the week, the doors being shut where the disciples were, for fear of the Jews, Jesus came and stood among them and said to them, "Peace be with you." When He had said this, he showed them His hands and His side. Then the disciples were glad when they saw the Lord. Jesus said to them again, "Peace be with you. As the Father has sent me, even so I send you." And when He had said this, He breathed on them, and said to them, "Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained."

or

John 15:26-27;16:12-15[Year B]

But when the Counselor comes, whom I shall send to you from the Father, even the Spirit of truth, who proceeds from the Father, he will bear witness to me; and you also are witnesses, because you have been with me from the beginning.

"I have yet many things to say to you, but you cannot bear them now. When the Spirit of truth comes, he will guide you into all the truth; for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come. He will glorify me, for he will take what is mine and declare it to you. All that the Father has is mine; therefore I said that he will take what is mine and declare it to you.

John 14:15-16, 23b-26 [Year C]

"If you love me, you will keep my commandments. And I will pray the Father, and he will give you another Counselor, to be with you for ever.

"If a man loves me, he will keep my word, and my Father will love him, and we will come to him and make our home with him. He who does not love me does not keep my words; and the word which you hear is not mine but the Father's who sent me. "These things I have spoken to you, while I am still with you. But the Counselor, the Holy Spirit, whom the Father will send in my name, he will teach you all things, and bring to your remembrance all that I have said to you.