Origination of Holy Spirit Very important topic! But first a humble correction: the non-biblical origin of Christianity's doctrines and rituals is indeed a teaching of some scholars, but they belong to a class of scholars called "liberals." Other just as qualified and credentialed scholars of academia hold alternative views, which allege a more conservative outlook. Greek origination of the doctrine of the Holy Spirit is therefore not an established fact.
The Holy Spirit of God is not the ghost of the dead Jesus. Rather, He is part of the Tri-unity of the Godhead (Trinity): Father, Son, and Holy Spirit. These are not three separate gods, but manifestations of the One true God. Ancient scholars used the illustration of the "Sun." The Sun manifests itself to Earth in two ways: heat and light. These represent the Spirit and Jesus who interact with earthlings. But they come from the One Sun, which represents the Father. One God manifested as a Tri-unity!
From time Immemorial To show that the Holy Spirit of God is not a conjecture nor manufacture of the later Greek philosophers, we need only go to the very first chapter of the very first book in the Holy Bible!
In the beginning God created the heavens and the earth...and the Spirit of God moved upon the face of the waters...(Genesis 1:1-2)
The Holy Spirit is seen to exist from the beginning of time...and before...since He was instrumental in the creation. From that chapter on, in the Bible, the Holy Spirit is mentioned as interacting with creation and creatures (men):
And the Lord said, "My Spirit shall not always strive with man for that he also is flesh..." (Genesis 6:3)
Cast me not away from Thy Presence, and take not Thy Holy Spirit from me. (Psalm 51:11, a prayer of David)
I (God) will come down and talk with thee there, and I will take of the Spirit which is upon thee, and will put it upon them...And the Lord came down in a cloud, and took of the Spirit that was upon him and gave it to the seventy elders, and it came to pass, they prophesied, and did not cease! (Numbers 11:17,25-29)
And Pharaoh said to his servants,"Can we find such a one as this is, a man in whom the Spirit of God is? (Genesis 41:38)
Then all the Midianites (armies)...pitched in the valley of Jezreel. But the Spirit of the LORD came upon Gideon and he blew a trumpet (call to arms)... (Judges 6:34)
And the Spirit of God came upon Azariah the son of Obed, and he went out to meet (King) Asa (to prophesy)...(2 Chronicles 15:1-2)
And they shall know that I am the LORD their God...Neither will I hide my face any more from them, for I have poured out My Spirit upon the House of Israel. saith the LORD God. (Ezekiel 39:28-29)
These scriptures dealt with events in eras before the Greeks. It is more than abundantly clear that the concept (reality) of the Holy Spirit was known long before the Greek Empire with its classical philosophers existed.
And that this same Holy Spirit was to continue interacting with mankind was voiced by the prophet Joel: In the latter days I will pour out My Spirit on all flesh. (See Acts 2) This Holy Spirit was seen as active in the Early Church (Christianity) and is taught throughout the Epistles of the Apostles. The Kingdom of God is not meat and drink (rituals), but righteousness, peace, and joy in the Holy Spirit! (Romans 14:17)
This is an important topic for struggling humanity in a world of differing philosophies vying for attention, and it is much appreciated that it was raised.