Have you tried explaining the Holy Spirit to a young child? Quite a challenge! We are of this planet, with feet squarely planted on dirt. The Holy Spirit is not! We are of flesh, mortal, physical, with aches and pains. He is not! A child processes reality through a fairly concrete perspective. The God of the Bible is not so concrete.
Jesus encountered a woman of the region of Samaria at a well one day. She belonged to that group of mixed-breed anomalies left over from the Assyrian deportations. The Samaritans were regarded by first century Hebrews as an aberrant cult to be avoided. The Samaritans revered Mt. Gerizim as the location of the holy habitation of the deity. Their understanding of God was limited since they had a truncated version of the Pentateuch and had syncretized those beliefs with some false teachings from the religions that had been transported to the area. The result was that they believed in a very concrete deity who was limited by physical domain and in some way was controlled by the sacrifices offered by the worshippers. Jesus exposed the error of this world-view by declaring, "God is spirit, and his worshipers must worship in spirit and in truth (John 4:24)." This worship would not be restricted by any physical site, since that is simply a false concept of the very nature of God. Worship must be in keeping with the spiritual nature of God (rather than physical constraint), and in keeping with his revealed truth (rather than human myth).
The Bible does not define 'spirit' for us, but it does offer descriptions. The Spirit of God is immortal, invisible and eternal, worthy of our giving honor and glory forever (1 Tim. 1:17). This Spirit lives in light that humans are unable to approach, "whom no one has seen or can see (1 Tim. 6:15-16)." The spiritual nature of God is difficult for us to understand since we have not yet seen him as he is, and apart from faith we are unable to understand that which we have not experienced. Our sensory perception does not offer any assistance in discerning the spiritual nature of God. God is not shackled by the bonds of physical matter.
I am now the ‘papa’ of six grandchildren. I do not even try to explain the spiritual nature of God to them. I am much better at telling them stories of the fantastic and marvelous things that the LORD has done. When we worship the God of the Bible, we worship one who is quite different from us, yet he desires to impart a portion of his spirit within us now as a foretaste of that day when we shall see him as he is and be able to approach the light when we cast off mortality and take on glorified immortality.