The Holy Spirit is one of three divine and distinct Persons that make up the One Eternal God. Each Person of the three is God, yet they exist together in a form we describe as the Holy Trinity. (CCC 685 i.e. Catechism of the Catholic Church)
Regardless of which divine Person (or Persons) may appear to be working at any given time or during any given event, the three Persons of the Trinity always act together, eternally united in a very special way. (CCC 266)
It may help to think of God the Father as the sovereign architect of all that is seen and unseen and of God the Son as the literal and personal expression of God’s infinite love and justice. You might think of God the Holy Spirit as the expression of the infinite love, which the Father has for the Son, and the Son for the Father, full of divine power, wisdom, glory and truth, as they all share in one and the same divine, godly “substance”.
There’s a great mystery here and much we can’t understand. Study the Bible and Catechism for the next 50 years or so and you might begin to appreciate the awesome nature and workings of the Holy Trinity.
Here’s how the concept of three persons in one God
might be mathematically expressed: 1 X 1 X 1 = 1.
We know the Holy Spirit as the Lord, the Giver of Life, who proceeds from the Father and the Son. (CCC 246)
He is the “Mighty Wind” who swept across the waters of the young earth and the “Breath of Life” who introduced Adam to his soul. (Genesis 1:2 and Genesis 2:7)
He guided pairs of every creature into Noah’s Ark and later, He personally opened the fountains of the great deep and the loosed the floodgates of heaven. (Genesis 7: 9 – 11)
He is the fiery Destroyer of Sodom and Gomorrah. (Genesis 19:24)
He is the One who quickened the infertile womb of Sarah, granting faithful Abraham a beloved son. (Genesis 18:14)
It is the Holy Spirit who hardened the heart of Pharao and who led the Israelites out of Egypt. He is the “Pillar of Cloud” and “Pillar of Fire” who protected His people in the desert and showed them the way. (Exodus 10:1 and Exodus 13:22)
The Holy Spirit is the strong “Burning Wind” who parted the Red Sea. (Exodus 14:21) He is the “Finger of God” who rendered the Ten Commandments in stone. (Exodus 31:18)
It was He who stopped up the River Jordan so His people could pass over on dry ground (Joshua 3:17) and it was He who caused the walls of Jericho to crumble. (Joshua 6:20)
The Holy Spirit guided the smooth, solitary stone that was launched by David’s sling, defeating Goliath, the hulking beast and mortal enemy of Israel.
(1st Samuel 17:49)
He has spoken through the Prophets (and inspired all the writers of the Bible).
To save His prophet Daniel, he sent an angel to shut the mouths of hungry lions. (Daniel 6:22)
With the consent of the Virgin Mary, He conceived the baby Jesus in her womb. (Luke 1:26)
He is the power behind every miracle. (Exodus 9:16, 2nd Kings 17:36, Psalms 77:14, Psalms 105:27, Isaiah 22:21, Jeremiah 16:21, Daniel 4:3, Matthew 9:2, Mark 1:27, Luke 1:35, Luke 4:14, Luke 4:36, Luke 5:17, Luke 9:44, Luke 10:19, Luke 24:49, John 1:12, John 17:2, Acts 1:8, Acts 4:33, Acts 10:38, Romans 1:3, Romans 9:17, Romans 13:1, Romans 15:13, Romans 15:19, 1st Corinthians 6:14, 2nd Corinthians 3:14, 1st Thessalonians 1:5, 1st Peter 4:14, 2nd Peter 1:3)
He dwelled within the Tabernacle in the desert (Exodus 33:9) and in the Holy of Holies on the Temple Mount in Jerusalem. (1st Kings 8:10)
Today, He sanctifies our Church (John 14:16) and dwells within every baptized, faithful and repentant Christian. (2nd Corinthians 6:16)
The Holy Spirit descended like a dove on the baptized Jesus (Matthew 3:16) and it was through the power of the Holy Spirit that Jesus, fully man and fully God, perfectly accomplished His divine mission.
Acts 10:38 Jesus of Nazareth: how God anointed him with the Holy Ghost and with power, who went about doing good and healing all that were oppressed by the devil, for God was with him.
It is the Holy Spirit who darkened the sky and shook the earth on Good Friday (Matthew 27:45) and 3 days hence, raised Himself from the dead. (Romans 8:11)
On Pentecost, visible as tongues of fire and audible as wind and thunder, He anointed Mary and the Apostles (and on all those gathered together with them), and presided at the birth of the Holy Catholic Church. (Acts 2:1)
He remains the Paraclete (advocate) and Spirit of Truth who guides the Church throughout history, protecting it from doctrinal error.
(John 14:16)
At Baptism, the Holy Spirit sweeps sin from our soul and takes up residence there, indelibly marking us as adopted children of God and co-heirs with Jesus Christ.
(Ephesians 4:30, Galatians 4:7)
At Mass, it is the Holy Spirit who transforms ordinary bread and wine into the glorified, resurrected body and blood of Jesus. (CCC 1375)
Through the other Sacraments, particularly Confirmation and Holy Orders, that same Spirit scribes additional marks, imparts special graces and bestows unique spiritual gifts.
(CCC 1317, CCC 1121, CCC 800)
Just before our Savior returns, the Holy Spirit will speak through God’s elect, revealing the “Man of Sin” (Antichrist, false-christ,) to all those with “eyes to see” and “ears to hear”. (2nd Thessalonians 2:3)
It is the Holy Spirit, who will, at the end of the age, transform our mortal bodies into glory and renovate the earth with holy fire, making all things new again.
(2nd Peter 3:7 -12, Revelation 21:1)
We know all this and more about the Holy Spirit because
it was revealed; first, by Jesus Christ and later, by
the Spirit Himself, who infallibly guides the Catholic Church,
from age to age.
I explain it as the part of Divinity that gives things the power to "change and move" (for lack of better terms), in the universe. The "Father, Son and Holy Spirit", are the 'different', (not "separate") aspects of the same 'Supreme Infinite Godhead', out of which all things arise. The Trinity signifies the Divine Attribute of 'Omnipresence', expressed as 'Creator', 'Created' and 'Creation', which are fundamental to our existence.
The Holy Spirit, I believe, is 'God's Love', that is around, in and through all of existence, by which 'everything, everywhere, at all times', is made.