"We" created beings live in the physical world. However, our world also has a spiritual side. Spiritual means more than just religious.

Physical is not spirit - Physical is what is seen and can be touched... worldly, earthly, temporal, relating to the body or flesh; bodily.

While we look not at the things which are seen, but at the things which are not seen: for the things which are seen are temporal [physical]; but the things which are not seen are eternal [spiritual]. 2 Corinthians 4:18

Spiritual is of the spirit - it is unseen... bodiless, ethereal, formless, immaterial, incorporeal, insubstantial, nonmaterial, nonphysical, unbodied, unsubstantial, such as thoughts, ideas, concepts, ambitions, desires, emotions.

"The Hebrew word for spirit is "ruwach" roo'-akh a primitive root; properly, to blow, i.e. breathe; only (literally) to smell or (by implication, perceive (figuratively, to anticipate, enjoy):--accept, smell, X touch, make of quick understanding" (Strongs Hebrew Dictionary).

Similarly, 'the Greek word is "pneuma" pnyoo'-mah from 4154; a current of air, i.e. breath (blast) or a breeze; by analogy or figuratively, a spirit, i.e. (human) the rational soul, (by implication) vital principle, mental disposition, etc., or (superhuman) an angel, demon, or (divine) God, Christ's spirit, the Holy Spirit:--ghost, life, spirit(-ual, -ually), mind. In the Greek, both "Ghost" and "Spirit" are translated from "pneuma"', so "Holy Ghost" and "Holy Spirit" are the same, "hagios pneuma" (Strongs Greek Dictionary).

Every living man has breath (spirit). Almost every living man has (some) understanding, thoughts, thus a spirit, a spiritual nature, even though living in a physical body. Thoughts and emotions (like the wind or breath) cannot be seen. They are spirit(ual).

Breath (spirit) does not exist outside a living creature (being). Thoughts and understanding do not exist outside a living person (human or divine). They can only belong to SOMEONE alive who has thoughts!

And יהוה [Yahweh] Elohim [god] formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul. Genesis 2:7

After Adam became a living soul, he possessed his own thoughts (spirit, mind, essence). That would be called Adam's spirit or the spirit of Adam. Adam's thoughts or the thoughts of Adam. Adam's essence or the essence of Adam. The spirit, essence, understanding of Adam is NOT a person separate from Adam, it is Adam's essence - his thoughts, desires, understanding. When Adam died his thoughts, his spirit, were no more.

Then shall the dust return to the earth as it was: and the spirit shall return unto Elohim who gave it. Ecclesiastes 12:7


Old Testament Spirits

In the Old Testament, "ghost" occurs only 11 times and it is never used as "Holy Ghost". In all instances it refers to dying, "giving up the ghost" which is equivalent to surrendering the spirit. No spirit (good, bad, holy or carnal) exists on its own. A spirit (the thoughts and essence) MUST belong to (be owned by) someone who has (possesses, owns) those thoughts! Someone must think the thoughts. Someone must possess the spirit. When men consider spiritual thoughts, they are in the spirit(ual). Spiritual does not (necessarily) mean religious. it means unseen. If man, who is physical can have a spirit, it is even easier to understand that a spirit being is and has a spirit. If the being is Holy, their spirit is Holy.

In the old testament this is quite clear, where "spirit" appears 235 times. In almost every case it refers to SOMEBODY'S spirit... my spirit, his spirit, thy spirit, your spirit, God's spirit, Joshua's spirit, Elijah's spirit, spirit of King Cyrus, the spirit of the Lord (the Lord's spirit), spirits of all flesh. Sometimes it refers to the spirits of knowledge, wisdom, mercy, jealousy (these of course are spirits / thoughts possessed by somebody), and there are a few evil spirits, familiar spirits and lying spirits. All these spirits are either spirits of men or spirits of a spirit (maybe better referred to as spirits with a body and spirits without a body?) The spirits that have no body are ALL either the spirit of the Father or the Son or good angels or evil spirits/angels (we only know about the nature of these. If there are men on other worlds, I don't know if they have physical bodies or are spiritual beings). The Son and good angels could have their own spirits, but they don't. Because they are at one with the Father, they all share the spirit of the Father. Even if it might be referred to as the spirit of the Messiah or the spirit of Gabriel, it is the Father's spirit dwelling within them. This should be our goal to possess the indwelling of the Father's spirit.

"Holy Spirit" occurs only three times in the Old Testament and in ALL cases it is THY Holy Spirit or HIS Holy Spirit (ie the spirit of Holy Yahweh). There is a handful of "spirit of the holy gods". (again, the spirit of Holy Yahweh). "Holy Ghost" is not mentioned at all. There is NO mention of any independent Spirit not owned or belonging to someone else (no independent third God).

Prior Jewish theology held that God's Spirit is merely the divine presence of God himself, whereas orthodox Christian theology holds that the Holy Spirit is a distinct person of God himself. (see wikipedia here)


New Testament Spirits

In contrast, the New Testament uses "ghost" almost exclusively with "the Holy Ghost" without reference to any owner - we aren't usually told to whom the spirit belongs. There are a handful of "ghost" references related to "giving up the ghost" (dying), especially at the death of the Son of Man. "Spirit" in the New Testament frequently refers to evil spirits, sometimes the Spirit of God or Holy Spirit.

The Old Testament teaches about what the spirit is and where it comes from and where it goes. By the New Testament everyone is assumed to know who is the owner of any spirit, especially the Holy Spirit / the Holy Ghost. Following is proof of this. We are told that "the Spirit of God" (the Spirit owned by God) is synonymous with "the Holy Ghost". How do we know that? The verse following says that the two are the same Spirit.

Wherefore I give you to understand, that no man speaking by the Spirit of God [ed. the Spirit owned by Yahweh] calleth Jesus accursed: and that no man can say that Jesus is the Lord, but by the Holy Ghost [ed. the Holy Ghost is thus far an unidentified Spirit, but we shouldn't need explanation]. Now there are diversities of gifts, but the same Spirit [ed. not a different spirit or one owned by someone else, but the same Spirit previously mentioned - the Spirit of God]. 1 Corinthians 12:3-4

We now have positive proof that the "Holy Ghost" is the "Spirit of God" which can also be called God's Spirit or the Holy Spirit. This proves that the supposed third person of the trinity is actually the Spirit of God or the Essence of God or God's thoughts, NOT a separate unidentified God with no name.


The Son's Holy Spirit

Now faith is the substance of things hoped for, the evidence of things not seen. Hebrews 11:1

Faith is the exercise of the spirit (the unseen). The Father is spirit(ual) only. The son before being born of Mary, was also spirit(ual) only. While on earth, the Son was man (physical/carnal), and possessed a human spirit. He had to set aside his spiritual invisible nature, his Holy spirit, and take on a physical, fleshly, visible nature. Except, His earthly spirit was the Father's spirit because the Father dwelt in Him and the two were as one.

The Bible uses the Father's Spirit and the Son's Spirit synonymously. It is frequently impossible to tell which actual Spirit is being discussed. But it really doesn't matter because their Spirits are the same. They are of One Spirit and One Mind. They are One. The Son was joined unto the Father.

What? know ye not that he which is joined to an harlot is one body? for two, saith he, shall be one flesh. But he that is joined unto יהוה [Yahweh] is one spirit. 1 Corinthians 6:16-17

We are told a little about the Son's Spirit. We do know that the Comforter is the Holy Ghost. We know that the Comforter is ALSO below (subordinate to) the Father because the Father sent him/it.

But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you. John 14:26

The Son possessed glory from the beginning. He set aside that glory to come to the earth as a baby.

I have glorified thee on the earth: I have finished the work which thou gavest me to do. And now, O Father, glorify thou me with thine own self with the glory which I had with thee before the world was. John 17:4-5

The glory that the Son set aside was His own Holy Spirit. His bodiless spirit (His Holy Spirit) ceased to exist when he was born as a carnal (but sinless) baby. Now, his new body possessed a new human spirit.

And when Yahushua had cried with a loud voice, he said, Father, into thy hands I commend my spirit: and having said thus, he gave up the Spirit. Luke 23:46

This spirit was the Son's Holy Spirit, not a separate person of godhead.

(But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.) John 7:39

After His resurrection he told Mary not to touch him, saying he had to ascend unto his Father.

Jesus saith unto her, Touch me not; for I am not yet ascended to my Father: but go to my brethren, and say unto them, I ascend unto my Father, and your Father; and to my God, and your God. John 20:17

What a triumphant, victorious homecoming that must have been! In Heaven, the Son was glorified and recovered his former estate. He received his glorified Holy Spirit. Now he could send back to earth the Comforter, His Holy Spirit. His thoughts, His power, His essence.

The Holy Spirit is never an independent, separate person as in the Trinity. It is the Spirit (thoughts, essence) of the glorified Christ which is also the Spirit of God (the Father's Spirit).