The Holy Ghost, or Holy Spirit is the third member of the Christian Trinity in most Christian religions - the divine triad of which the Holy Ghost was the third member.
     The Christian Holy Ghost descended as a dove and alighted on Christ’s head at his baptism. That the Holy Ghost us seen in the shape of a bird – a dove or a pigeon – is a very ancient pagan tradition. In the ancient Syrian temple of Hierapolis, Semiramis is shown with a dove on her head. .In Rome a dove. or pigeon. was a legendary spirit, the accompaniment of Venus, the emblem of female procreative energy.. The dove and the pigeon were used interchangeably.       
      The Hebrew Ruh Elohim, translated "Spirit of God", is more acurately, Wind of the Gods. The word Pneuma, in the Greek New Testament, is used for Spirit, Holy Ghost, Breath and Wind so that in the Christian Scriptures they are synonymous.is sometimes translated Ghost and sometimes Wind, as suites the fancy of the translators.  In John 3:5 the word is Spirit, in verse eight both Wind and Spirit, and in Luke 1:35 the term is Holy Ghost.

In these triads the third member Holy Ghost, Holy Breath and Holy Wind were equivalent terms for the sigh from the mouth of the Supreme God, as laid down in pagan traditions. The Holy Wind is suggested by the mighty rushing wind from heaven which filled the house on the day of Pentecost (Acts 2:2). The Holy Wind is an accepted term for the Holy Ghost in ancient religions.  In the Theban Trinity, Khonso was inferior to Arion and Mant. In the Hindu triad, Siva was subordinate to Brahma and Vishnu. The Holy Ghost conception in the Christian world corresponds with these older ideas. It has always stood third in rank after the Father and the Son or the Word, a slave doing all the hard work and getting little worshipt. Today it is still seldom addressed in Christian devotion.
     The Holy Ghost was the Holy Breath which, in the Hindu traditions, moved upon the face of the waters at creation, and imparted vitality into everything created. A similar conception appears in the scriptures. In Psalms 33:6 the Word of the Lord made the heavens, and all the host of them by the breath of his mouth. The Brahminical conception of creation by the Divine Breath, the Holy Ghost, which was breathed into Adam to make him a living soul. The Prana or principle of life of the Hindus is the breath of life by which the Brahma, the Creator, animates the clay to make man a living soul.
     The Holy Ghost appears also as a tongue of fire, which sat upon each of the apostles in Acts 2:3.
     Buddha, an incarnate God of the Hindus over two thousand years ago, is often seen with a glory or tongue of fire upon his head. The visible form of the Holy Ghost as fire was accepted among the Buddhists, Druids and Etrurians. The Holy Ghost, or Holy Spirit when visible, was in the form of fire or a bird and was always accompanied with wisdom and power. The Hindus, Persians and Chaldeans made offerings to fire, emblem of the Holy Ghost or Holy Spirit as the solar fire.
     Holy men of God, like some of the prophets, are considered inspired by the Holy Ghost (2 Peter 1:21; Acts 28:25). The ancient Celts were moved by the Holy Ghost and also claimed that their Salic laws (seventy-two in number) were inspired by the Salo Ghost or Holy Ghost, known also as the Wisdom of the Spirit, or the Voice of the Spirit.
     The Holy Ghost being imparted by the laying on of hands is also an ancient custom. By the putting hands on the head of the candidate, the Celts conveyed the Holy Ghost or Holy Spirit.
     Baptism by or into the Holy Ghost accompanied with fire (Matt 3:2) is also traceable to a very ancient period. The Tuscans, or Etrurians, baptized with fire, wind (ghost) and water. Baptism into the first member of the Trinity, the Father, was with fire: baptism into the second member of the Trinity, the Word, was with water: baptism into the third member of the Trinity, the Holy Ghost or Holy Spirit, was with breath, gas, ghost, wind, or spirit. In ancient countries,a young child was taken to the priest to name him before the sacred fire. There he was sprinkled with holy water from a vessel made of the sacred tree known as the Holme. To impart the Holy Ghost by breathing (as in John 20:22), the priest blew his breath upon the child to transfer the Holy Ghost, thus baptising the child by air, spiritus sanctus or ghost. The practice of breathing in or upon was quite common among the ancient heathen.
     The Holy Ghost as the agent in divine conception, or the procreation of other Gods. Jesus is said to have been conceived by the Holy Ghost (Matt 1:18), and we find similar claims of divine procreation via the Holy Ghost in the old religions. In the Hindu myths, Sakya was conceived by the Holy Ghost Nara-an.
     The origin of the tradition of the Holy Ghost is easily traced to the Brahminical trifold conception of God. First is the god of power or might, Brahma or Brahm, the Father, second is the god of creation, the Word  (as in the creative Word: John 1:3), third is the god of generation and regeneration, the Holy Spirit or Holy Ghost. Under the Brahminical theocracy, the Holy Ghost was the living, vital, active, life-imparting agent.
     The Holy Ghost in the Christian Scripture is the agent of Christ’s conception, because, as Matthew declares, he was conceived by the Holy Ghost. The Holy Ghost was also the regenerating agent at his baptism, although Luke, who relates it, does not say why the Holy Spirit in the form of a bird, alit upon his head. The reason is nevertheless fully disclosed in the older mythical religions. Christians claim baptism imparts a new spiritual life—they are born again. This new spirit appeared as a dove or a pigeon.
     The Spirit was originally female so that the Trinity consisted of two masculine principles and a feminine one, the latter being the procreative or regenerative principle. Around 200 AD  the Holy Ghost ceased to be referred toi as female but as neuter, and then, later, as male
     The primary windy idea of the Holy Ghost is traceable to that early period of society when the untutored people of the earth in their ignorance of nature easily believed that movement signified the passage of a god.
     The Buddhists had their god Vasus, who manifested himself as fire, wind, storms, gas, ghosts, gusts, and the breath, thus being nearly a counterpart of the Christian Holy Ghost. This god sprang from the supreme, primordial God, who was to Brahmins and Buddhists a fine, spiritual substance—aura, anima, wind, ether, igneous fluid, or electrical fire or fire from the sun, giving rise to baptism by fire. The third member of the Trinity, subsequently seems to have arisen from this being and had the same properties.
     What was a sin against the Holy Ghost and why was it unpardonable? It was refusing to allow the Holy Ghost to effect the second birth. Since baptism by whatever means into the Holy Ghost was the only means of redeeming sins against the Father or the Son, the refusal or prevention of baptism meant there could be no forgiveness. It was the only route so could not be avoided if sin was to be pardoned. An offence committed against the third limb of the Godhead barred the door to forgiveness, in this life or that to come. To sin against the Holy Ghost was to block the path by which the door of heaven was to be reached.