In Lesson 2 of the classic Unity text, Lessons in Truth, H. Emilie Cady wrote:
When Jesus was talking with the Samaritan woman at the well, He said to her, “God is Spirit: and they that worship him must worship in spirit and truth.” (John 4:24 A.V. reads, “God is a Spirit,” but the marginal note is, “God is Spirit,” and some other versions render this passage, “God is Spirit.”) To say “a Spirit” would be to imply the existence of more than one Spirit. Jesus, in His statement, did not imply this.
Webster in his definition of Spirit says: “In the abstract, life or consciousness viewed as an independent type of existence. One manifestation of the divine nature; the Holy Spirit.”
God, then, is not, as many of us have been taught to believe, a big personage or man residing somewhere in a beautiful region in the sky, called “heaven,” where good people go when they die, and see Him clothed in ineffable glory; nor is He a stern, angry judge only awaiting opportunity somewhere to punish bad people who have failed to live a perfect life here.
God is Spirit, or the creative energy that is the cause of all visible things. God as Spirit is the invisible life and intelligence underlying all physical things. There could be no body, or visible part, to anything unless there was first Spirit as creative cause.
Can we be sure that the Webster dictionary definition is what the author of the fourth Gospel meant by Spirit? The Authorised Version of the Bible (A. V.), the version usually referred to today as the King James Version, is a translation prepared under the instruction of King James I of England (VI of Scotland). Could the 19th century American dictionary referred to by H. Emilie Cady in the above quotation be providing the meaning of spirit intended by the 17th century English translators? Maybe. Maybe not.
According to an article in Wikipedia, King James had given the translators instructions intended to guarantee that the new version would conform to the ecclesiology and reflect the episcopal structure of the Church of England and its belief in an ordained clergy. Such instructions would tend to bias any translation. We need to check the early Greek sources if we wish to know what the author of the gospel meant.
The word translated as spirit is the Greek pneuma meaning wind or breath. It has the same meaning as the Hebrew ruach. Referring to these meanings, Marcus Borg has written:
The associations of both are suggestive. Both are invisible yet manifestly real. We cannot see the wind, though its presence and effects are felt; it moves without being seen. When it blows, it is all around us. Breath is like wind inside the body. For the ancient Hebrews (as for us), it was associated with life. Metaphorically, God as Spirit is both wind and breath, a nonmaterial reality outside of us and within us. Our breath is God breathing us, and God is as near to us as our own breath. Speaking of God as Spirit, as both wind and breath, evokes both transcendence and nearness.
Karen Armstrong comments:
The early Jewish Christians used the term [Holy Spirit] to describe the immanent divine force within them that filled them with an empowering energy and enabled them to understand the deeper meaning of Jesus’s mission.
Spirit, then, is like the wind. Even when the wind is so light we do not notice it, it is there. We breathe it in: it fills us and keeps us alive, invigorated. We breathe it out: we share our out-breath with all that is and enliven all of creation.
The Hebrew scriptures generally use the word ruach in the phrase ruach elohim or breath of the Gods. Spirit is not the whole of God. God is beyond human explanation or description. Spirit/breath is but an aspect of God, the immanence of God.
 H. Emilie Cady (1896) Lessons in Truth, Unity Books
 Marcus J. Borg (1997) The God We Never Knew, HarperOne
 Karen Armstrong (2009) The Case for God, Knopf