Jesus Christ revealed to us the mystery of the Father, Son, and Holy Spirit (Matthew 28:19-20), known as the Holy Trinity in the Tradition of the Church. The Holy Spirit is one of three persons in one God - God the Father, the Son Jesus Christ, and the Holy Spirit. The Holy Ghost, as he is called in early New Testament texts, is a mystery. Both God the Father and the Lord Jesus Christ speak often in Scripture, but the Holy Spirit directly speaks only in the Acts of the Apostles (8:29, 10:19-20, 13:2).
The Hebrew word ruaḥ signifies wind, breath, or spirit in Hebrew Scripture, as in Genesis 1:2. The Miserere Psalm 51:11 is translated: "Do not cast me away from your presence, and do not take your holy spirit from me." The Book of the Prophet Isaiah noted the spirit of the Lord will rest upon a descendent of Jesse, and instill him with wisdom, understanding, counsel, knowledge, fortitude, piety, and fear of the Lord (Isaiah 11:1-3). The Church calls these the Gifts of the Holy Spirit.
The Holy Spirit is named with the Father and the Son in the Great Commission in the Gospel of Matthew (28:19-20), and appears like a dove in the Baptism of Jesus in the River Jordan in Mark 1:9-11. He overshadows the Virgin Mary in the Infancy Narrative of Jesus at the Annunciation in Luke 1:35, and is referred to as the Counselor or Paraclete in John 14:16. We learn in the Gospel of John that the Holy Spirit can only come after the death and Resurrection of our Lord (16:7).
The Acts of the Apostles is often called the Gospel of the Holy Spirit. Just before the Ascension of our Lord 40 days after his Resurrection, Christ announces the promise of the Father that the Holy Spirit will come upon the Apostles to be his witnesses to the ends of the earth. Ten days later, the Descent of the Holy Spirit at Pentecost (Acts 2:1-4) empowers the Apostles to spread the Word.
During St. Paul's second missionary journey (Acts 16:7-12), the Spirit of Jesus - πνεῦμα Ἰησοῦ - redirected Paul and Luke to Macedonia, a journey which was the first recorded introduction of Christianity into Europe! St. Paul wrote that our bodies are temples of the Holy Spirit in First Corinthians 6:19 and described the Manifestation of the Spirit in First Corinthians 12:7-11. He described the Fruit of the Spirit in Galatians 5:22-23 - love, joy, peace, patience, kindness, generosity, faithfulness, gentleness, and self-control. St. Peter offered important roles of the Spirit in First Peter 1:12 and Second Peter 1:20-21. Here are a few noteworthy Biblical passages on the Holy Spirit:
Go therefore and make disciples of all nations,
baptizing them in the name of the Father and of the Son and of the Holy Spirit,
teaching them to observe all that I have commanded you;
and lo, I am with you always, to the close of the age."
Gospel of Matthew 28:19-20
It happened in those days that Jesus came from Nazareth of Galilee and was baptized in the Jordan by John.
On coming up out of the water he saw the heavens being torn open and the Spirit, like a dove, descending upon him.
And a voice came from the heavens, “You are my beloved Son; with you I am well pleased.”
Gospel of Mark 1:9-11
Then the angel said to her, "Do not be afraid, Mary, for you have found favor with God.
Behold, you will conceive in your womb and bear a son, and you shall name him Jesus.
He will be great and will be called Son of the Most High,
and the Lord God will give him the throne of David his father,
and he will rule over the house of Jacob forever, and of his kingdom there will be no end."
But Mary said to the angel, "How can this be, since I have no relations with a man?"
And the angel said to her in reply, "The Holy Spirit will come upon you,
and the power of the Most High will overshadow you.
Therefore the child to be born will be called holy, the Son of God.
Gospel of Luke 1:30-35
"For the Holy Spirit will teach you at that moment what you should say."
Gospel of Luke 12:12
And John bore witness,
"I saw the Spirit descend as a dove from heaven, and it remained on him.
I myself did not know him; but he who sent me to baptize with water said to me,
'He on whom you see the Spirit descend and remain,
this is he who baptizes with the Holy Spirit.'
And I have seen and have borne witness that this is the Son of God."
Gospel of John 1:32-34
Jesus answered, "Truly, truly, I say unto you,
unless you be born again of the water and the Spirit,
you cannot enter into the kingdom of God"
Gospel of John 3:5
On the last day of the feast, the great day, Jesus stood up and proclaimed,
"If any one thirst, let him come to me and drink.
He who believes in me, as the scripture has said,
'Out of his heart shall flow rivers of living water [Ezekiel 36:25].'"
Now this he said about the Spirit, which those who believed in him were to receive;
for as yet the Spirit had not been given, because Jesus was not yet glorified.
Gospel of John 7:37-39
"And I will pray the Father, and he will give you another Counselor,
to be with you for ever,
even the Spirit of truth, whom the world cannot receive,
because it neither sees him nor knows him;
you know him, for he dwells with you, and will be in you."
Gospel of John 14:16-17
"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.
Peace I leave with you; my peace I give to you;
not as the world gives do I give to you."
Gospel of John 14:26-27
"When the Advocate comes whom I will send you from the Father,
the Spirit of truth that proceeds from the Father, he will testify to me."
Gospel of John 15:26
"Nevertheless I tell you the truth: it is to your advantage that I go away,
for if I do not go away,
the Counselor will not come to you; but if I go, I will send him to you.
And when he comes, he will convince the world concerning sin and righteousness and judgment.
Gospel of John 16:7-8
"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."
Gospel of John 16:13-15
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."
Gospel of John 20:21-23
"When the time for Pentecost was fulfilled, they were all in one place together.
And suddenly there came from the sky a noise like a strong driving wind,
and it filled the entire house in which they were.
Then there appeared to them tongues as of fire,
which parted and came to rest on each one of them.
And they were all filled with the Holy Spirit and began to speak in different tongues,
as the Spirit enabled them to proclaim."
Acts of the Apostles 2:1-4
Then the Spirit said to Philip, "Go up and join this chariot."
Acts of the Apostles 8:29
And while Peter was pondering the vision, the Spirit said to him, "Behold, three men are looking for you.
Rise and go down, and accompany them without hesitation; for I have sent them."
Acts of the Apostles 10:19-20
The Holy Spirit said, "Set apart for me Barnabas and Saul for the work to which I have called them."
Acts of the Apostles 13:2
If the Spirit of the one who raised Jesus from the dead dwells in you,
the one who raised Christ from the dead will give life to your mortal bodies also,
through his Spirit that dwells in you.
Epistle of St. Paul to the Romans 8:11
Do you not know that your body is a temple of the Holy Spirit within you,
whom you have from God, and that you are not your own?
First Letter of St. Paul to the Corinthians 6:19
But to each one is given the manifestation of the Spirit for the common good.
For to one is given the word of wisdom through the Spirit,
and to another the word of knowledge according to the same Spirit;
to another faith by the same Spirit, and to another gifts of healing by the one Spirit,
and to another the effecting of miracles, and to another prophecy, and to another the distinguishing of spirits,
to another various kinds of tongues, and to another the interpretation of tongues.
But one and the same Spirit works all these things, distributing to each one individually just as He wills.
The First Letter of St. Paul to the Corinthians 12:7-11
Now He who establishes us with you in Christ and anointed us is God,
who also sealed us and gave us the Spirit in our hearts as a pledge.
The Second Letter of St. Paul to the Corinthians 1:21-22
In contrast, the fruit of the Spirit is love, joy, peace, patience, kindness, generosity, faithfulness, gentleness, self-control.
Against such there is no law.
Now those who belong to Christ Jesus have crucified their flesh with its passions and desires.
If we live in the Spirit, let us also follow the Spirit.
St. Paul to the Galatians 5:22-25
It was revealed to them that they were serving not themselves but you,
in the things which have now been announced to you by those who preached the good news to you
through the Holy Spirit sent from heaven, things into which angels long to look.
First Letter of St. Peter 1:12
Knowing this first, that no prophecy of scripture is of private interpretation.
For no prophecy ever came by the will of man:
but men spoke from God, being moved by the Holy Spirit.
Second Letter of St. Peter 1:20-21